<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:5729ef46-c855-4d8f-885b-a3786bbd3677,g:1eef8250-6d7c-4bfc-8e23-e3d39fd7c7ee-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://telos.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="tls-20251231.xsd#CONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://telos.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6157dacd-0d45-44df-8e3a-cee50befca9d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_StatementTable_6157dacd-0d45-44df-8e3a-cee50befca9d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_e511a27b-9e7f-4ac3-9030-8ffded21e93e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6157dacd-0d45-44df-8e3a-cee50befca9d" xlink:to="loc_srt_ProductOrServiceAxis_e511a27b-9e7f-4ac3-9030-8ffded21e93e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_e511a27b-9e7f-4ac3-9030-8ffded21e93e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_e511a27b-9e7f-4ac3-9030-8ffded21e93e" xlink:to="loc_srt_ProductsAndServicesDomain_e511a27b-9e7f-4ac3-9030-8ffded21e93e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_725fc5a1-32d2-487f-9579-377e1d91a26c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_e511a27b-9e7f-4ac3-9030-8ffded21e93e" xlink:to="loc_srt_ProductsAndServicesDomain_725fc5a1-32d2-487f-9579-377e1d91a26c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_9293fc18-5f7a-46bb-80d9-bfa60fce0110" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_725fc5a1-32d2-487f-9579-377e1d91a26c" xlink:to="loc_us-gaap_ServiceMember_9293fc18-5f7a-46bb-80d9-bfa60fce0110" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_3b6b9cc9-76ef-471b-ad10-1ba05a04ee74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_725fc5a1-32d2-487f-9579-377e1d91a26c" xlink:to="loc_us-gaap_ProductMember_3b6b9cc9-76ef-471b-ad10-1ba05a04ee74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ad7284bb-6b15-4cba-bc8e-7dd5f312920c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ad7284bb-6b15-4cba-bc8e-7dd5f312920c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_7abff022-f826-49f0-92fd-8138d9a1dee2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_7abff022-f826-49f0-92fd-8138d9a1dee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_780f4e09-46a7-42f5-b8c6-3365ab23c319" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductionRelatedImpairmentsOrCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_780f4e09-46a7-42f5-b8c6-3365ab23c319" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_fd3a32b3-4e07-4a6b-a313-e86f33e2a97f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_fd3a32b3-4e07-4a6b-a313-e86f33e2a97f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_d1a9ed7a-e6d5-4dbc-9335-372de2d9a63f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_d1a9ed7a-e6d5-4dbc-9335-372de2d9a63f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_ba5b34e2-0699-4bd0-b8aa-50b5b6f212c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_GrossProfit_ba5b34e2-0699-4bd0-b8aa-50b5b6f212c1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_65d5e974-bc32-4e29-bc75-8c646b971cdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_65d5e974-bc32-4e29-bc75-8c646b971cdb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_ad14ef74-7e64-4b47-92ec-a288d28db878" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_ad14ef74-7e64-4b47-92ec-a288d28db878" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019ba301-2b7d-78b4-a5f5-b42c845e7234" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019ba301-2b7d-78b4-a5f5-b42c845e7234" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_64494458-edcc-4494-af92-c0220485a4ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_64494458-edcc-4494-af92-c0220485a4ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_b8e32b32-5a7f-4ae5-9eb9-a80650526d64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_f501a266-a7b0-43ef-b530-3c01053b9f08" xlink:to="loc_us-gaap_OperatingExpenses_b8e32b32-5a7f-4ae5-9eb9-a80650526d64" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_8490984f-1e37-40d0-9cee-929bdc4de57a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_OperatingIncomeLoss_8490984f-1e37-40d0-9cee-929bdc4de57a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_0d390111-1283-4442-8c65-3cebfcb4f43a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_0d390111-1283-4442-8c65-3cebfcb4f43a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_ce2cb0d7-5070-4c19-b4a2-bd23d2184763" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_InterestExpenseNonoperating_ce2cb0d7-5070-4c19-b4a2-bd23d2184763" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_02ced74c-de2d-4d25-bcaa-f62a81f57833" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_02ced74c-de2d-4d25-bcaa-f62a81f57833" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_c7a99f76-9901-4c57-ae18-2c4f3db48dfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_c7a99f76-9901-4c57-ae18-2c4f3db48dfb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_dffad515-091c-4761-8101-762e8247001c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_NetIncomeLoss_dffad515-091c-4761-8101-762e8247001c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_8e6ef3db-17b8-4a1c-9f55-9fc5f3a0592d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_EarningsPerShareAbstract_8e6ef3db-17b8-4a1c-9f55-9fc5f3a0592d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_d99cada4-32ef-4e55-a2d0-34f6d482be7e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_8e6ef3db-17b8-4a1c-9f55-9fc5f3a0592d" xlink:to="loc_us-gaap_EarningsPerShareBasic_d99cada4-32ef-4e55-a2d0-34f6d482be7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_49f00550-e845-4bb2-a484-7d5a1d83947d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_8e6ef3db-17b8-4a1c-9f55-9fc5f3a0592d" xlink:to="loc_us-gaap_EarningsPerShareDiluted_49f00550-e845-4bb2-a484-7d5a1d83947d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_f975fc30-3443-4cb3-b071-c31ecb335a2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_ce92cfd9-cbfb-41e8-9904-506d6ecabb3f" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_f975fc30-3443-4cb3-b071-c31ecb335a2d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_a9e163cb-609d-41ce-a727-9243c3961a94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_f975fc30-3443-4cb3-b071-c31ecb335a2d" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_a9e163cb-609d-41ce-a727-9243c3961a94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_d785a998-c367-4698-9d1d-11cc9861f3b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_f975fc30-3443-4cb3-b071-c31ecb335a2d" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_d785a998-c367-4698-9d1d-11cc9861f3b7" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="tls-20251231.xsd#CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://telos.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_5bf49c7a-df26-4aaa-a44b-004f3d7ddae5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_c5b8eaba-5e15-460f-999e-d775e11a7fef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_5bf49c7a-df26-4aaa-a44b-004f3d7ddae5" xlink:to="loc_us-gaap_StatementTable_c5b8eaba-5e15-460f-999e-d775e11a7fef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_a089f019-3754-4371-92f1-9b19bc8faaae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_c5b8eaba-5e15-460f-999e-d775e11a7fef" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_a089f019-3754-4371-92f1-9b19bc8faaae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a089f019-3754-4371-92f1-9b19bc8faaae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a089f019-3754-4371-92f1-9b19bc8faaae" xlink:to="loc_us-gaap_EquityComponentDomain_a089f019-3754-4371-92f1-9b19bc8faaae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_432bd96d-a05b-4b09-981e-33dc142f9637" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a089f019-3754-4371-92f1-9b19bc8faaae" xlink:to="loc_us-gaap_EquityComponentDomain_432bd96d-a05b-4b09-981e-33dc142f9637" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_591915a8-93d7-4a31-a7a2-e7c6e4d074d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_432bd96d-a05b-4b09-981e-33dc142f9637" xlink:to="loc_us-gaap_CommonStockMember_591915a8-93d7-4a31-a7a2-e7c6e4d074d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_39d2b230-26f3-43aa-a554-40139135a882" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_432bd96d-a05b-4b09-981e-33dc142f9637" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_39d2b230-26f3-43aa-a554-40139135a882" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d4a0ab1f-ec4f-440d-8afc-2756c778050a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_432bd96d-a05b-4b09-981e-33dc142f9637" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_d4a0ab1f-ec4f-440d-8afc-2756c778050a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_75f6c1ea-9201-47e9-9058-bfe8caf5190a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_432bd96d-a05b-4b09-981e-33dc142f9637" xlink:to="loc_us-gaap_RetainedEarningsMember_75f6c1ea-9201-47e9-9058-bfe8caf5190a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5bf49c7a-df26-4aaa-a44b-004f3d7ddae5" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_06ab2e94-45f4-4eb2-82a5-2d52c222dd1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_06ab2e94-45f4-4eb2-82a5-2d52c222dd1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4bd579bd-adb3-411b-ab1a-564cfd3556ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockholdersEquity_4bd579bd-adb3-411b-ab1a-564cfd3556ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_cc89c0fe-ab1f-4e5c-ad84-b037e18e260a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_NetIncomeLoss_cc89c0fe-ab1f-4e5c-ad84-b037e18e260a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_2058fa08-ffdf-4c36-881b-410811d89187" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_2058fa08-ffdf-4c36-881b-410811d89187" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_25376082-14d4-43ff-a31d-9edec99a9b1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPortionAttributableToParent_25376082-14d4-43ff-a31d-9edec99a9b1b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_5ab873d6-9e4e-49a6-87fe-ed351b7112bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_5ab873d6-9e4e-49a6-87fe-ed351b7112bc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_e12eab32-0a15-4a15-9484-95048ccab6e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_RestrictedStockSharesIssuedNetOfSharesForTaxWithholdings_e12eab32-0a15-4a15-9484-95048ccab6e1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings_c47bd4f6-a359-40e0-b4fc-62f60aa56dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_RestrictedStockValueSharesIssuedNetOfTaxWithholdings_c47bd4f6-a359-40e0-b4fc-62f60aa56dfa" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_fd6469e9-9a83-4494-8529-50d1fb797734" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_fd6469e9-9a83-4494-8529-50d1fb797734" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_ab9871eb-f9af-4958-aa65-81c1147f9f9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_ab9871eb-f9af-4958-aa65-81c1147f9f9c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_019cb343-9486-7def-83f7-900b587292df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_019cb343-9486-7def-83f7-900b587292df" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_dc80cdb3-abbe-430d-b95b-8c21c1911186" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_dc80cdb3-abbe-430d-b95b-8c21c1911186" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f6c04975-bead-457a-a2bd-6f3339c7ee3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_f6c04975-bead-457a-a2bd-6f3339c7ee3b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_b6381a24-a3a8-47a0-8502-adf4942854ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5dd56288-b6ea-42d4-8dd5-2fa32fb6f71d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_b6381a24-a3a8-47a0-8502-adf4942854ea" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_da20e796-983b-43db-ba80-a7f579b2b1ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_fd3795cf-a0e7-4550-961d-bd8ba20d0642" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/ORGANIZATIONDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#ORGANIZATIONDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/ORGANIZATIONDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_c4396c2e-6198-447e-b070-02e20339c326" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_8f1da138-e61a-4ebc-94ca-780200e09fd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_c4396c2e-6198-447e-b070-02e20339c326" xlink:to="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_8f1da138-e61a-4ebc-94ca-780200e09fd8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_759356fa-f067-42c2-be97-f7eff3b31d95" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetTable_8f1da138-e61a-4ebc-94ca-780200e09fd8" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_759356fa-f067-42c2-be97-f7eff3b31d95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_759356fa-f067-42c2-be97-f7eff3b31d95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_759356fa-f067-42c2-be97-f7eff3b31d95" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_759356fa-f067-42c2-be97-f7eff3b31d95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3f3f0bac-0c38-4c90-b573-ab9734b3da2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_759356fa-f067-42c2-be97-f7eff3b31d95" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3f3f0bac-0c38-4c90-b573-ab9734b3da2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_TelosIdMember_0241635f-edb8-4549-9510-eb33b5ba4a3d" xlink:href="tls-20251231.xsd#tls_TelosIdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3f3f0bac-0c38-4c90-b573-ab9734b3da2b" xlink:to="loc_tls_TelosIdMember_0241635f-edb8-4549-9510-eb33b5ba4a3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_55722483-fddf-43b6-8021-1beb004dff96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidationLessThanWhollyOwnedSubsidiaryParentOwnershipInterestEffectsOfChangesNetLineItems_c4396c2e-6198-447e-b070-02e20339c326" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_55722483-fddf-43b6-8021-1beb004dff96" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c5a3a-dbbd-7e17-8854-a556ec971896" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_srt_RangeAxis_019c5a3a-dbbd-7e17-8854-a556ec971896" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c5a3a-dbbd-7e17-8854-a556ec971896_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c5a3a-dbbd-7e17-8854-a556ec971896" xlink:to="loc_srt_RangeMember_019c5a3a-dbbd-7e17-8854-a556ec971896_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c5a3a-dbbd-7ef4-a270-1885876067a1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c5a3a-dbbd-7e17-8854-a556ec971896" xlink:to="loc_srt_RangeMember_019c5a3a-dbbd-7ef4-a270-1885876067a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c5a3a-dbbd-74e0-8abf-810221ef7d45" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c5a3a-dbbd-7ef4-a270-1885876067a1" xlink:to="loc_srt_MinimumMember_019c5a3a-dbbd-74e0-8abf-810221ef7d45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c5a3a-dbbd-76d0-85ce-d2238dd25e72" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c5a3a-dbbd-7ef4-a270-1885876067a1" xlink:to="loc_srt_MaximumMember_019c5a3a-dbbd-76d0-85ce-d2238dd25e72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c5a3a-dbbd-7522-8976-0f095590debf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c5a3a-dbbd-7522-8976-0f095590debf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c5a3a-dbbd-7522-8976-0f095590debf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c5a3a-dbbd-7522-8976-0f095590debf" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c5a3a-dbbd-7522-8976-0f095590debf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c5a3a-dbbd-707f-915c-6b7c11936ae4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c5a3a-dbbd-7522-8976-0f095590debf" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c5a3a-dbbd-707f-915c-6b7c11936ae4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019c5a3a-dbbd-74d3-8ac7-ff43f71c63bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c5a3a-dbbd-707f-915c-6b7c11936ae4" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019c5a3a-dbbd-74d3-8ac7-ff43f71c63bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019c5a3b-5805-7bdc-bbc8-890101aef140" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_us-gaap_AwardTypeAxis_019c5a3b-5805-7bdc-bbc8-890101aef140" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c5a3b-5805-7bdc-bbc8-890101aef140_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019c5a3b-5805-7bdc-bbc8-890101aef140" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c5a3b-5805-7bdc-bbc8-890101aef140_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c5a3b-5805-73f9-bba1-a7d793da0aae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019c5a3b-5805-7bdc-bbc8-890101aef140" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c5a3b-5805-73f9-bba1-a7d793da0aae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019c5a3b-5805-7e7d-8f26-1e185999e357" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c5a3b-5805-73f9-bba1-a7d793da0aae" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019c5a3b-5805-7e7d-8f26-1e185999e357" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ServiceBasedRSUAwardsMember_019c5a3b-5805-76f8-aa89-ccb165ec91c1" xlink:href="tls-20251231.xsd#tls_ServiceBasedRSUAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019c5a3b-5805-73f9-bba1-a7d793da0aae" xlink:to="loc_tls_ServiceBasedRSUAwardsMember_019c5a3b-5805-76f8-aa89-ccb165ec91c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019c5a3b-5805-7558-ad16-a3576992ae40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_us-gaap_PlanNameAxis_019c5a3b-5805-7558-ad16-a3576992ae40" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019c5a3b-5805-7558-ad16-a3576992ae40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019c5a3b-5805-7558-ad16-a3576992ae40" xlink:to="loc_us-gaap_PlanNameDomain_019c5a3b-5805-7558-ad16-a3576992ae40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019c5a3b-5805-7d55-98af-52371125f8b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019c5a3b-5805-7558-ad16-a3576992ae40" xlink:to="loc_us-gaap_PlanNameDomain_019c5a3b-5805-7d55-98af-52371125f8b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_Two016OmnibusLongTermIncentivePlanMember_019c5a3b-5805-7f62-b0cb-bcbfb4abbf65" xlink:href="tls-20251231.xsd#tls_Two016OmnibusLongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019c5a3b-5805-7d55-98af-52371125f8b6" xlink:to="loc_tls_Two016OmnibusLongTermIncentivePlanMember_019c5a3b-5805-7f62-b0cb-bcbfb4abbf65" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_019c5a3b-84b8-71e7-9a1e-2d8833586825" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_019c5a3b-84b8-71e7-9a1e-2d8833586825" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c5a3b-84b8-71e7-9a1e-2d8833586825_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c5a3b-84b8-71e7-9a1e-2d8833586825" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c5a3b-84b8-71e7-9a1e-2d8833586825_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_019c5a3b-84b8-7068-94be-a4fedf5c2de0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_019c5a3b-84b8-71e7-9a1e-2d8833586825" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_019c5a3b-84b8-7068-94be-a4fedf5c2de0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_019c5a3b-84b8-7d72-acc5-6d331061dc1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_019c5a3b-84b8-7068-94be-a4fedf5c2de0" xlink:to="loc_us-gaap_EmployeeSeveranceMember_019c5a3b-84b8-7d72-acc5-6d331061dc1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_019c5a3b-84b8-740d-90fd-73afbded94e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_us-gaap_RestructuringPlanAxis_019c5a3b-84b8-740d-90fd-73afbded94e8" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-740d-90fd-73afbded94e8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c5a3b-84b8-740d-90fd-73afbded94e8" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-740d-90fd-73afbded94e8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-7430-90ca-24b97da18e24" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_019c5a3b-84b8-740d-90fd-73afbded94e8" xlink:to="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-7430-90ca-24b97da18e24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_A2022RestructuringPlanMember_019c5a3b-84b8-7968-a550-4e0a05504a94" xlink:href="tls-20251231.xsd#tls_A2022RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-7430-90ca-24b97da18e24" xlink:to="loc_tls_A2022RestructuringPlanMember_019c5a3b-84b8-7968-a550-4e0a05504a94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_A2024RestructuringPlanMember_019c5a3b-84b8-75c2-aaac-8c0255f921d8" xlink:href="tls-20251231.xsd#tls_A2024RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-7430-90ca-24b97da18e24" xlink:to="loc_tls_A2024RestructuringPlanMember_019c5a3b-84b8-75c2-aaac-8c0255f921d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_A2025RestructuringPlanMember_019c5a3b-a5af-7b83-8f7f-8db527820a64" xlink:href="tls-20251231.xsd#tls_A2025RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_019c5a3b-84b8-7430-90ca-24b97da18e24" xlink:to="loc_tls_A2025RestructuringPlanMember_019c5a3b-a5af-7b83-8f7f-8db527820a64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c5a3b-84b8-7364-8327-05ec698b9cd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_180fa7c4-0234-482a-9e3f-0380f9ee737b" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c5a3b-84b8-7364-8327-05ec698b9cd6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c5a3b-84b8-7364-8327-05ec698b9cd6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c5a3b-84b8-7364-8327-05ec698b9cd6" xlink:to="loc_us-gaap_SegmentDomain_019c5a3b-84b8-7364-8327-05ec698b9cd6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c5a3b-84b8-70af-8e60-e6da37eb0de7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c5a3b-84b8-7364-8327-05ec698b9cd6" xlink:to="loc_us-gaap_SegmentDomain_019c5a3b-84b8-70af-8e60-e6da37eb0de7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecuritySolutionsSegmentMember_019c5a3b-84b8-75a7-ae3e-28be8a430074" xlink:href="tls-20251231.xsd#tls_SecuritySolutionsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c5a3b-84b8-70af-8e60-e6da37eb0de7" xlink:to="loc_tls_SecuritySolutionsSegmentMember_019c5a3b-84b8-75a7-ae3e-28be8a430074" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecureNetworksSegmentMember_019c5a3b-84b8-7263-ad53-20942c1b0949" xlink:href="tls-20251231.xsd#tls_SecureNetworksSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c5a3b-84b8-70af-8e60-e6da37eb0de7" xlink:to="loc_tls_SecureNetworksSegmentMember_019c5a3b-84b8-7263-ad53-20942c1b0949" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019c5a3a-dbbd-7d8d-9816-2f5b08bae6ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019c5a3a-dbbd-7d8d-9816-2f5b08bae6ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019c5a3a-f91b-7204-a9a5-3daa47760a9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_019c5a3a-f91b-7204-a9a5-3daa47760a9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_019c5a3b-12bc-7509-916b-5d5e76895789" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_019c5a3b-12bc-7509-916b-5d5e76895789" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedComputerSoftwareNet_019c5a3b-12bc-7337-b6c3-31d00c31395a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedComputerSoftwareNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_CapitalizedComputerSoftwareNet_019c5a3b-12bc-7337-b6c3-31d00c31395a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_019c5a3b-3b79-7dc5-b53c-92efaf6c79c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_AdvertisingExpense_019c5a3b-3b79-7dc5-b53c-92efaf6c79c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019c5a3b-5805-762f-afe0-74c123680dd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_019c5a3b-5805-762f-afe0-74c123680dd5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019c5a3b-5805-73b7-a51e-e6e745fc95f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019c5a3b-5805-73b7-a51e-e6e745fc95f6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_019c5a3b-84b8-773b-a5e6-d3a638f9951f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostCostIncurredToDate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_RestructuringAndRelatedCostCostIncurredToDate1_019c5a3b-84b8-773b-a5e6-d3a638f9951f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_019c5a3b-a5af-7ba4-aa40-6bbadf540eec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_019c5a3b-a5af-7ba4-aa40-6bbadf540eec" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_GoodwillAmortizedAndDeductedOverPeriod_019c5aaa-0aa9-76c5-9654-6eff29674dd9" xlink:href="tls-20251231.xsd#tls_GoodwillAmortizedAndDeductedOverPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_tls_GoodwillAmortizedAndDeductedOverPeriod_019c5aaa-0aa9-76c5-9654-6eff29674dd9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringIncurredCostStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_019cd4f8-4383-7104-aade-17861c680113" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringIncurredCostStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_RestructuringIncurredCostStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_019cd4f8-4383-7104-aade-17861c680113" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportingUnits_019cde7f-9aaf-7c26-93ee-8467bd21b59c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfReportingUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_NumberOfReportingUnits_019cde7f-9aaf-7c26-93ee-8467bd21b59c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_019cde8e-0751-7b2a-88be-998f1e7816e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_019c5a3a-dbbd-7395-99bd-4383e450c14c" xlink:to="loc_us-gaap_RestructuringCharges_019cde8e-0751-7b2a-88be-998f1e7816e8" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESRestructuringExpensesandImpairmentLossDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESRestructuringExpensesandImpairmentLossDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESRestructuringExpensesandImpairmentLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_4e520a49-75b4-40a7-b005-43fe1bc18d83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_4e520a49-75b4-40a7-b005-43fe1bc18d83" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_00ec4ae4-61bb-4dc3-9fe7-b2a00d78a3fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_4e520a49-75b4-40a7-b005-43fe1bc18d83" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_00ec4ae4-61bb-4dc3-9fe7-b2a00d78a3fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_00ec4ae4-61bb-4dc3-9fe7-b2a00d78a3fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_00ec4ae4-61bb-4dc3-9fe7-b2a00d78a3fb" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_00ec4ae4-61bb-4dc3-9fe7-b2a00d78a3fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_dcddba8f-0e6d-4d1e-9f43-7c44ee982c24" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_00ec4ae4-61bb-4dc3-9fe7-b2a00d78a3fb" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_dcddba8f-0e6d-4d1e-9f43-7c44ee982c24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_b5d54479-67b9-446f-9b35-7deb487a6bf3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_dcddba8f-0e6d-4d1e-9f43-7c44ee982c24" xlink:to="loc_us-gaap_CostOfSalesMember_b5d54479-67b9-446f-9b35-7deb487a6bf3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ResearchAndDevelopmentSellingGeneralAndAdministrativeExpensesMember_f1b5fff5-561f-4588-a519-0bbfc686e717" xlink:href="tls-20251231.xsd#tls_ResearchAndDevelopmentSellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_dcddba8f-0e6d-4d1e-9f43-7c44ee982c24" xlink:to="loc_tls_ResearchAndDevelopmentSellingGeneralAndAdministrativeExpensesMember_f1b5fff5-561f-4588-a519-0bbfc686e717" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_5318fc01-e1d2-466c-90c7-e250d883a038" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_SeveranceCosts1_5318fc01-e1d2-466c-90c7-e250d883a038" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringCosts_5aaad6d1-3764-4ab2-8ee7-7d61269bbaf1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_OtherRestructuringCosts_5aaad6d1-3764-4ab2-8ee7-7d61269bbaf1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_832dc4f7-5a04-4d96-80cf-1726275d57dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_RestructuringCharges_832dc4f7-5a04-4d96-80cf-1726275d57dd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_f12482e1-32eb-4537-a2a3-d8e1550b4e66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_f12482e1-32eb-4537-a2a3-d8e1550b4e66" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringSettlementAndImpairmentProvisions_ea789d33-9479-4e1a-8169-fe54978ab26e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringSettlementAndImpairmentProvisions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_RestructuringSettlementAndImpairmentProvisions_ea789d33-9479-4e1a-8169-fe54978ab26e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_92f87563-66fc-4d96-b144-667d1a7ee22e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_AssetImpairmentCharges_92f87563-66fc-4d96-b144-667d1a7ee22e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_a619bf3a-d4a1-4dd8-be1b-283159376576" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductionRelatedImpairmentsOrCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_6a8fc68f-b93a-4fbe-9838-939f617c47af" xlink:to="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_a619bf3a-d4a1-4dd8-be1b-283159376576" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESChangesinRestructuringExpensesAccrualDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESChangesinRestructuringExpensesAccrualDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESChangesinRestructuringExpensesAccrualDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_97779a27-8547-4c22-b5cb-0df6bed62e42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_49d101b9-11e0-46a1-b82b-342e0abe0871" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_97779a27-8547-4c22-b5cb-0df6bed62e42" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_49d101b9-11e0-46a1-b82b-342e0abe0871" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_a3ea2d62-12e7-4b37-afbd-edcc523ad3e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_49d101b9-11e0-46a1-b82b-342e0abe0871" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_a3ea2d62-12e7-4b37-afbd-edcc523ad3e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_a3ea2d62-12e7-4b37-afbd-edcc523ad3e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_a3ea2d62-12e7-4b37-afbd-edcc523ad3e4" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_a3ea2d62-12e7-4b37-afbd-edcc523ad3e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_19992d58-34eb-4a53-bdbe-3ca67bcd6847" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_a3ea2d62-12e7-4b37-afbd-edcc523ad3e4" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_19992d58-34eb-4a53-bdbe-3ca67bcd6847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_50081979-f385-433b-935f-90c3f9b07815" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_19992d58-34eb-4a53-bdbe-3ca67bcd6847" xlink:to="loc_us-gaap_EmployeeSeveranceMember_50081979-f385-433b-935f-90c3f9b07815" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_be2822f0-44e9-45f4-b2b8-ab2660cd5ac2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_97779a27-8547-4c22-b5cb-0df6bed62e42" xlink:to="loc_us-gaap_RestructuringReserveRollForward_be2822f0-44e9-45f4-b2b8-ab2660cd5ac2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_0901b73a-d5ef-48d3-b7bf-54becb8100a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_be2822f0-44e9-45f4-b2b8-ab2660cd5ac2" xlink:to="loc_us-gaap_RestructuringReserve_0901b73a-d5ef-48d3-b7bf-54becb8100a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_96d68799-e6d5-493b-810c-d5f9e2df2513" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_be2822f0-44e9-45f4-b2b8-ab2660cd5ac2" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_96d68799-e6d5-493b-810c-d5f9e2df2513" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_907f06d8-2268-4b46-abb8-9ba855799278" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_be2822f0-44e9-45f4-b2b8-ab2660cd5ac2" xlink:to="loc_us-gaap_PaymentsForRestructuring_907f06d8-2268-4b46-abb8-9ba855799278" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_777c73fd-0ba6-4653-bfca-957eb52f1803" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/REVENUERECOGNITIONNarrativeDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#REVENUERECOGNITIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/REVENUERECOGNITIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4700af77-a379-4d72-9d81-b1977ce731c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4700af77-a379-4d72-9d81-b1977ce731c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08f37939-bfcb-42a7-a881-318197c02b85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08f37939-bfcb-42a7-a881-318197c02b85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember_d8b50eed-7ad8-4e97-a713-6d49b5aa1208" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08f37939-bfcb-42a7-a881-318197c02b85" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember_d8b50eed-7ad8-4e97-a713-6d49b5aa1208" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_025ddfd7-da4e-44ff-93d5-2c0479d65867_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_025ddfd7-da4e-44ff-93d5-2c0479d65867_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_c753fc29-80d8-4342-9494-aed7c588463d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_c753fc29-80d8-4342-9494-aed7c588463d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_RevenueTimingOfTransferOfGoodsOrServiceMember_74173ae5-05a0-46fa-bf84-d3778623ad72" xlink:href="tls-20251231.xsd#tls_RevenueTimingOfTransferOfGoodsOrServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_c753fc29-80d8-4342-9494-aed7c588463d" xlink:to="loc_tls_RevenueTimingOfTransferOfGoodsOrServiceMember_74173ae5-05a0-46fa-bf84-d3778623ad72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_1e4923c0-ae3d-4a05-b6de-10bc72b442ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:to="loc_us-gaap_TransferredOverTimeMember_1e4923c0-ae3d-4a05-b6de-10bc72b442ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_9dc571a8-6007-4466-bce7-a1214c0822c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_9dc571a8-6007-4466-bce7-a1214c0822c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_e9cbb270-562f-4d33-9b7e-32853aa11ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_e9cbb270-562f-4d33-9b7e-32853aa11ff8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_76dd8a43-27a1-48b0-9043-ef81bdfa152f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_76dd8a43-27a1-48b0-9043-ef81bdfa152f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueModificationOfContract_ccff7f10-8b0d-46e0-99af-e162daeb14ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueModificationOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueModificationOfContract_ccff7f10-8b0d-46e0-99af-e162daeb14ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_1c34fc3d-9f80-48a7-b4a2-8eff2f33ee03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_1c34fc3d-9f80-48a7-b4a2-8eff2f33ee03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_7acb8cb0-0677-4c15-acd0-102abce0c0c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_7acb8cb0-0677-4c15-acd0-102abce0c0c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_c77c7312-5b3f-4698-a9a5-5f3dd5dc8eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_c77c7312-5b3f-4698-a9a5-5f3dd5dc8eaf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5cac69c4-a2a9-488f-8f20-2e4e5f927518" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5cac69c4-a2a9-488f-8f20-2e4e5f927518" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_84a3e015-0f15-4513-b381-4f3b6ec86f16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_84a3e015-0f15-4513-b381-4f3b6ec86f16" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/REVENUERECOGNITIONNarrativeDetails_1" xlink:type="simple" xlink:href="tls-20251231.xsd#REVENUERECOGNITIONNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://telos.com/role/REVENUERECOGNITIONNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4700af77-a379-4d72-9d81-b1977ce731c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_4700af77-a379-4d72-9d81-b1977ce731c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08f37939-bfcb-42a7-a881-318197c02b85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_4700af77-a379-4d72-9d81-b1977ce731c5" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08f37939-bfcb-42a7-a881-318197c02b85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember_d8b50eed-7ad8-4e97-a713-6d49b5aa1208" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_08f37939-bfcb-42a7-a881-318197c02b85" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember_d8b50eed-7ad8-4e97-a713-6d49b5aa1208" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_025ddfd7-da4e-44ff-93d5-2c0479d65867_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_025ddfd7-da4e-44ff-93d5-2c0479d65867_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_c753fc29-80d8-4342-9494-aed7c588463d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_025ddfd7-da4e-44ff-93d5-2c0479d65867" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_c753fc29-80d8-4342-9494-aed7c588463d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_RevenueTimingOfTransferOfGoodsOrServiceMember_74173ae5-05a0-46fa-bf84-d3778623ad72" xlink:href="tls-20251231.xsd#tls_RevenueTimingOfTransferOfGoodsOrServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_c753fc29-80d8-4342-9494-aed7c588463d" xlink:to="loc_tls_RevenueTimingOfTransferOfGoodsOrServiceMember_74173ae5-05a0-46fa-bf84-d3778623ad72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_32204c35-90a5-4214-9c07-35deb30a91ac" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimingOfTransferOfGoodOrServiceDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceAxis_b071a5a4-c45f-40ad-a2b8-7d4c6ef27396" xlink:to="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredOverTimeMember_1e4923c0-ae3d-4a05-b6de-10bc72b442ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferredOverTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:to="loc_us-gaap_TransferredOverTimeMember_1e4923c0-ae3d-4a05-b6de-10bc72b442ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransferredAtPointInTimeMember_9dc571a8-6007-4466-bce7-a1214c0822c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransferredAtPointInTimeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TimingOfTransferOfGoodOrServiceDomain_3c33cfb6-a2b5-4097-abc7-005325720764" xlink:to="loc_us-gaap_TransferredAtPointInTimeMember_9dc571a8-6007-4466-bce7-a1214c0822c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_76dd8a43-27a1-48b0-9043-ef81bdfa152f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_76dd8a43-27a1-48b0-9043-ef81bdfa152f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueModificationOfContract_ccff7f10-8b0d-46e0-99af-e162daeb14ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueModificationOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueModificationOfContract_ccff7f10-8b0d-46e0-99af-e162daeb14ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_1c34fc3d-9f80-48a7-b4a2-8eff2f33ee03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss_1c34fc3d-9f80-48a7-b4a2-8eff2f33ee03" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_7acb8cb0-0677-4c15-acd0-102abce0c0c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_7acb8cb0-0677-4c15-acd0-102abce0c0c6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_c77c7312-5b3f-4698-a9a5-5f3dd5dc8eaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_c77c7312-5b3f-4698-a9a5-5f3dd5dc8eaf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5cac69c4-a2a9-488f-8f20-2e4e5f927518" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5cac69c4-a2a9-488f-8f20-2e4e5f927518" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_84a3e015-0f15-4513-b381-4f3b6ec86f16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2944a08e-98dd-4d8b-9e26-9ba18ec7697e" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_84a3e015-0f15-4513-b381-4f3b6ec86f16" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/REVENUERECOGNITIONScheduleofRevenuebyCustomerTypeDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#REVENUERECOGNITIONScheduleofRevenuebyCustomerTypeDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/REVENUERECOGNITIONScheduleofRevenuebyCustomerTypeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_e153135b-c3d2-4e8e-a92a-a566ed4019b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_e153135b-c3d2-4e8e-a92a-a566ed4019b9" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_5dea1e5b-576a-4dbd-8d71-4056e2c1ec92" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:to="loc_srt_MajorCustomersAxis_5dea1e5b-576a-4dbd-8d71-4056e2c1ec92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_5dea1e5b-576a-4dbd-8d71-4056e2c1ec92_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_5dea1e5b-576a-4dbd-8d71-4056e2c1ec92" xlink:to="loc_srt_NameOfMajorCustomerDomain_5dea1e5b-576a-4dbd-8d71-4056e2c1ec92_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_78f26444-1e40-4561-95b5-c74c42765567" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_5dea1e5b-576a-4dbd-8d71-4056e2c1ec92" xlink:to="loc_srt_NameOfMajorCustomerDomain_78f26444-1e40-4561-95b5-c74c42765567" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_FederalGovernmentMember_daf7af04-aae6-4130-8002-9c8bfb4b498c" xlink:href="tls-20251231.xsd#tls_FederalGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_78f26444-1e40-4561-95b5-c74c42765567" xlink:to="loc_tls_FederalGovernmentMember_daf7af04-aae6-4130-8002-9c8bfb4b498c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_StateLocalAndCommercialMember_9ca95e67-5e88-45f6-886b-31790ada3144" xlink:href="tls-20251231.xsd#tls_StateLocalAndCommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_78f26444-1e40-4561-95b5-c74c42765567" xlink:to="loc_tls_StateLocalAndCommercialMember_9ca95e67-5e88-45f6-886b-31790ada3144" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a2679dd1-c2dc-48ed-bd97-d891f03c2041" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a2679dd1-c2dc-48ed-bd97-d891f03c2041" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a2679dd1-c2dc-48ed-bd97-d891f03c2041_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a2679dd1-c2dc-48ed-bd97-d891f03c2041" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_a2679dd1-c2dc-48ed-bd97-d891f03c2041_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_051e0e42-917e-419f-b3c5-00879ff7dfd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_a2679dd1-c2dc-48ed-bd97-d891f03c2041" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_051e0e42-917e-419f-b3c5-00879ff7dfd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember_500cdad6-b233-4f40-bb47-d2634329f66b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_051e0e42-917e-419f-b3c5-00879ff7dfd5" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember_500cdad6-b233-4f40-bb47-d2634329f66b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerSegmentBenchmarkMember_fd681bb4-e027-49ad-9fda-2d230332e93b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerSegmentBenchmarkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_051e0e42-917e-419f-b3c5-00879ff7dfd5" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerSegmentBenchmarkMember_fd681bb4-e027-49ad-9fda-2d230332e93b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_a42ba511-e1da-4e7f-88a5-f53b0e4f338f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_a42ba511-e1da-4e7f-88a5-f53b0e4f338f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_a42ba511-e1da-4e7f-88a5-f53b0e4f338f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_a42ba511-e1da-4e7f-88a5-f53b0e4f338f" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_a42ba511-e1da-4e7f-88a5-f53b0e4f338f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_f808e8d5-089d-48d0-b23e-a358db26ded1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_a42ba511-e1da-4e7f-88a5-f53b0e4f338f" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_f808e8d5-089d-48d0-b23e-a358db26ded1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_4ef2875a-9934-4481-b66d-14db5bd7729f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_f808e8d5-089d-48d0-b23e-a358db26ded1" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_4ef2875a-9934-4481-b66d-14db5bd7729f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_53579039-da9c-4c40-9bc0-7a80931abdb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_53579039-da9c-4c40-9bc0-7a80931abdb0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_53579039-da9c-4c40-9bc0-7a80931abdb0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_53579039-da9c-4c40-9bc0-7a80931abdb0" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_53579039-da9c-4c40-9bc0-7a80931abdb0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_9eb40dd4-292d-41ba-9fa9-0cec03c889d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerBasisOfPricingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingAxis_53579039-da9c-4c40-9bc0-7a80931abdb0" xlink:to="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_9eb40dd4-292d-41ba-9fa9-0cec03c889d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedPriceContractMember_8c32371e-7c8c-4db1-b667-7868887ca454" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedPriceContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_9eb40dd4-292d-41ba-9fa9-0cec03c889d3" xlink:to="loc_us-gaap_FixedPriceContractMember_8c32371e-7c8c-4db1-b667-7868887ca454" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TimeAndMaterialsContractMember_1a87f342-dc07-48b5-acc3-4559ebb4c201" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TimeAndMaterialsContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_9eb40dd4-292d-41ba-9fa9-0cec03c889d3" xlink:to="loc_us-gaap_TimeAndMaterialsContractMember_1a87f342-dc07-48b5-acc3-4559ebb4c201" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_CostPlusFixedFeeMember_e1f02f88-aa0a-49a0-8c0e-10005cec7c4d" xlink:href="tls-20251231.xsd#tls_CostPlusFixedFeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContractWithCustomerBasisOfPricingDomain_9eb40dd4-292d-41ba-9fa9-0cec03c889d3" xlink:to="loc_tls_CostPlusFixedFeeMember_e1f02f88-aa0a-49a0-8c0e-10005cec7c4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_246438ba-da93-41f8-bc91-2cd08c333c5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_006cef4c-4763-4f33-a032-f5c3af93c34c" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_246438ba-da93-41f8-bc91-2cd08c333c5c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_246438ba-da93-41f8-bc91-2cd08c333c5c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_246438ba-da93-41f8-bc91-2cd08c333c5c" xlink:to="loc_us-gaap_SegmentDomain_246438ba-da93-41f8-bc91-2cd08c333c5c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_fa678143-6058-43b3-833c-ef499cd99c2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_246438ba-da93-41f8-bc91-2cd08c333c5c" xlink:to="loc_us-gaap_SegmentDomain_fa678143-6058-43b3-833c-ef499cd99c2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecuritySolutionsSegmentMember_b3f05b7e-854d-42ed-a896-3e37573c9aec" xlink:href="tls-20251231.xsd#tls_SecuritySolutionsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_fa678143-6058-43b3-833c-ef499cd99c2d" xlink:to="loc_tls_SecuritySolutionsSegmentMember_b3f05b7e-854d-42ed-a896-3e37573c9aec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecureNetworksSegmentMember_0d002155-440e-4e11-ade2-88a91740465e" xlink:href="tls-20251231.xsd#tls_SecureNetworksSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_fa678143-6058-43b3-833c-ef499cd99c2d" xlink:to="loc_tls_SecureNetworksSegmentMember_0d002155-440e-4e11-ade2-88a91740465e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ced249b2-87d2-4b67-9477-8e20358f59cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_e153135b-c3d2-4e8e-a92a-a566ed4019b9" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_ced249b2-87d2-4b67-9477-8e20358f59cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_60a1cfde-56d0-4c77-9d61-f4866ad88614" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_e153135b-c3d2-4e8e-a92a-a566ed4019b9" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_60a1cfde-56d0-4c77-9d61-f4866ad88614" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/ACCOUNTSRECEIVABLENETNarrativeDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#ACCOUNTSRECEIVABLENETNarrativeDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/ACCOUNTSRECEIVABLENETNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_17774c2e-9adc-46d5-b977-34103c0d4cc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a787a3b1-3d5e-47c3-8473-b0c5e5783368" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_17774c2e-9adc-46d5-b977-34103c0d4cc5" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a787a3b1-3d5e-47c3-8473-b0c5e5783368" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_12d7a5a4-2498-4da3-93de-21f906b5f2ae" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a787a3b1-3d5e-47c3-8473-b0c5e5783368" xlink:to="loc_srt_MajorCustomersAxis_12d7a5a4-2498-4da3-93de-21f906b5f2ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_12d7a5a4-2498-4da3-93de-21f906b5f2ae_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_12d7a5a4-2498-4da3-93de-21f906b5f2ae" xlink:to="loc_srt_NameOfMajorCustomerDomain_12d7a5a4-2498-4da3-93de-21f906b5f2ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_49625e14-3474-4c7e-a452-b702db09b417" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_12d7a5a4-2498-4da3-93de-21f906b5f2ae" xlink:to="loc_srt_NameOfMajorCustomerDomain_49625e14-3474-4c7e-a452-b702db09b417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_FederalGovernmentMember_d70395bd-0270-4b5c-93f0-14e1e736b3ff" xlink:href="tls-20251231.xsd#tls_FederalGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_49625e14-3474-4c7e-a452-b702db09b417" xlink:to="loc_tls_FederalGovernmentMember_d70395bd-0270-4b5c-93f0-14e1e736b3ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_fa1ac684-30d2-4025-9816-7a889f344562" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a787a3b1-3d5e-47c3-8473-b0c5e5783368" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_fa1ac684-30d2-4025-9816-7a889f344562" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fa1ac684-30d2-4025-9816-7a889f344562_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_fa1ac684-30d2-4025-9816-7a889f344562" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_fa1ac684-30d2-4025-9816-7a889f344562_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_113443cd-e2df-4d24-863e-c3b99c52ccb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_fa1ac684-30d2-4025-9816-7a889f344562" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_113443cd-e2df-4d24-863e-c3b99c52ccb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_67e6389b-d5c6-4632-b39b-fa5157671d89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_113443cd-e2df-4d24-863e-c3b99c52ccb4" xlink:to="loc_us-gaap_AccountsReceivableMember_67e6389b-d5c6-4632-b39b-fa5157671d89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_26399624-668a-4bab-bb41-d50453cda53f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a787a3b1-3d5e-47c3-8473-b0c5e5783368" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_26399624-668a-4bab-bb41-d50453cda53f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_26399624-668a-4bab-bb41-d50453cda53f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_26399624-668a-4bab-bb41-d50453cda53f" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_26399624-668a-4bab-bb41-d50453cda53f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_2a508683-d5c1-4f2c-8cc1-a442fb78a62d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_26399624-668a-4bab-bb41-d50453cda53f" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_2a508683-d5c1-4f2c-8cc1-a442fb78a62d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_979fd446-7b80-4eb4-8c3a-868c2283d580" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_2a508683-d5c1-4f2c-8cc1-a442fb78a62d" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_979fd446-7b80-4eb4-8c3a-868c2283d580" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019ce53d-d646-7deb-9d44-554706796678" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a787a3b1-3d5e-47c3-8473-b0c5e5783368" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019ce53d-d646-7deb-9d44-554706796678" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019ce53d-d646-7deb-9d44-554706796678_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019ce53d-d646-7deb-9d44-554706796678" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019ce53d-d646-7deb-9d44-554706796678_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019ce53d-d646-74ca-8a70-ff2e8d1ffb82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019ce53d-d646-7deb-9d44-554706796678" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019ce53d-d646-74ca-8a70-ff2e8d1ffb82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019ce53d-d646-717d-a003-983771fc1ab2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019ce53d-d646-74ca-8a70-ff2e8d1ffb82" xlink:to="loc_us-gaap_SubsequentEventMember_019ce53d-d646-717d-a003-983771fc1ab2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_9e675f96-9396-48d5-b5d0-16fae05215c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_17774c2e-9adc-46d5-b977-34103c0d4cc5" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_9e675f96-9396-48d5-b5d0-16fae05215c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ReceivablesSoldUnderFactoringAgreement_e2d2db07-244c-45df-8502-73724341dc74" xlink:href="tls-20251231.xsd#tls_ReceivablesSoldUnderFactoringAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_17774c2e-9adc-46d5-b977-34103c0d4cc5" xlink:to="loc_tls_ReceivablesSoldUnderFactoringAgreement_e2d2db07-244c-45df-8502-73724341dc74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_PurchaseReceivablesMaximumLimit_019ce83a-a7e6-7f94-a22e-14b5944f996c" xlink:href="tls-20251231.xsd#tls_PurchaseReceivablesMaximumLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_17774c2e-9adc-46d5-b977-34103c0d4cc5" xlink:to="loc_tls_PurchaseReceivablesMaximumLimit_019ce83a-a7e6-7f94-a22e-14b5944f996c" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/PROPERTYANDEQUIPMENTNETDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#PROPERTYANDEQUIPMENTNETDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/PROPERTYANDEQUIPMENTNETDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_fb6a30d1-a48f-402a-9d49-375fab31a7d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_d53dd0d2-0958-4874-a640-d851ddb5f65b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_fb6a30d1-a48f-402a-9d49-375fab31a7d0" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_d53dd0d2-0958-4874-a640-d851ddb5f65b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f78cc38f-aabb-4179-b777-dcfa7ed52aab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_d53dd0d2-0958-4874-a640-d851ddb5f65b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f78cc38f-aabb-4179-b777-dcfa7ed52aab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f78cc38f-aabb-4179-b777-dcfa7ed52aab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f78cc38f-aabb-4179-b777-dcfa7ed52aab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f78cc38f-aabb-4179-b777-dcfa7ed52aab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bd97f2e3-5ff5-4f20-8e88-fbe16f998ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_f78cc38f-aabb-4179-b777-dcfa7ed52aab" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bd97f2e3-5ff5-4f20-8e88-fbe16f998ca2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_FurnitureAndEquipmentMember_79fa91f8-0eb0-405b-9f77-035eced84599" xlink:href="tls-20251231.xsd#tls_FurnitureAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bd97f2e3-5ff5-4f20-8e88-fbe16f998ca2" xlink:to="loc_tls_FurnitureAndEquipmentMember_79fa91f8-0eb0-405b-9f77-035eced84599" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_2e6ed684-44ab-4e5c-a28f-c8c6a5c3e6be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bd97f2e3-5ff5-4f20-8e88-fbe16f998ca2" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_2e6ed684-44ab-4e5c-a28f-c8c6a5c3e6be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_46dc6939-032f-47ae-883b-66e56211dc4d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_fb6a30d1-a48f-402a-9d49-375fab31a7d0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_46dc6939-032f-47ae-883b-66e56211dc4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_0449a9b6-581b-49dc-957d-1e4c1032bc9f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_fb6a30d1-a48f-402a-9d49-375fab31a7d0" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_0449a9b6-581b-49dc-957d-1e4c1032bc9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_0aa32d76-6c8c-426b-a93e-842c4adb0780" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_fb6a30d1-a48f-402a-9d49-375fab31a7d0" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_0aa32d76-6c8c-426b-a93e-842c4adb0780" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDepreciationAndAmortization_c687d8a6-5bba-4969-b5bf-b052ee2dc7b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_fb6a30d1-a48f-402a-9d49-375fab31a7d0" xlink:to="loc_us-gaap_OtherDepreciationAndAmortization_c687d8a6-5bba-4969-b5bf-b052ee2dc7b5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/GOODWILLNETScheduleofCarryingAmountofGoodwillbyReportableSegmentsDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#GOODWILLNETScheduleofCarryingAmountofGoodwillbyReportableSegmentsDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/GOODWILLNETScheduleofCarryingAmountofGoodwillbyReportableSegmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_019b8e70-d5c5-7298-a540-320d93517561" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_019b8e70-d5c5-79b7-adb6-9e5bf47f8ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_019b8e70-d5c5-7298-a540-320d93517561" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_019b8e70-d5c5-79b7-adb6-9e5bf47f8ef0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019b8e70-d5c5-7734-8141-aa84893babdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_019b8e70-d5c5-79b7-adb6-9e5bf47f8ef0" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019b8e70-d5c5-7734-8141-aa84893babdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019b8e70-d5c5-7734-8141-aa84893babdf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019b8e70-d5c5-7734-8141-aa84893babdf" xlink:to="loc_us-gaap_SegmentDomain_019b8e70-d5c5-7734-8141-aa84893babdf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019b8e70-d5c5-7277-ba3f-10c80c1b3257" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019b8e70-d5c5-7734-8141-aa84893babdf" xlink:to="loc_us-gaap_SegmentDomain_019b8e70-d5c5-7277-ba3f-10c80c1b3257" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecuritySolutionsSegmentMember_019b8e71-7254-7f6d-bd4d-37caa52cffc7" xlink:href="tls-20251231.xsd#tls_SecuritySolutionsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019b8e70-d5c5-7277-ba3f-10c80c1b3257" xlink:to="loc_tls_SecuritySolutionsSegmentMember_019b8e71-7254-7f6d-bd4d-37caa52cffc7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecureNetworksSegmentMember_019b8e74-e609-79bc-9cd4-973e7f7a3cb2" xlink:href="tls-20251231.xsd#tls_SecureNetworksSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019b8e70-d5c5-7277-ba3f-10c80c1b3257" xlink:to="loc_tls_SecureNetworksSegmentMember_019b8e74-e609-79bc-9cd4-973e7f7a3cb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillRollForward_019b8e77-fdd9-7ba2-addb-cddae286b598" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_019b8e70-d5c5-7298-a540-320d93517561" xlink:to="loc_us-gaap_GoodwillRollForward_019b8e77-fdd9-7ba2-addb-cddae286b598" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019b8e70-d5c5-7cef-9ad6-a14766f7eb25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019b8e77-fdd9-7ba2-addb-cddae286b598" xlink:to="loc_us-gaap_Goodwill_019b8e70-d5c5-7cef-9ad6-a14766f7eb25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019b8e73-fddd-7940-a877-79e566be2ffd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillRollForward_019b8e77-fdd9-7ba2-addb-cddae286b598" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019b8e73-fddd-7940-a877-79e566be2ffd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019b8e78-7ece-78d3-bc5b-4bc2db72965b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/INTANGIBLEASSETSNETScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#INTANGIBLEASSETSNETScheduleofFiniteLivedIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/INTANGIBLEASSETSNETScheduleofFiniteLivedIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_cea82096-5986-4335-9970-a1816714625f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_54f43e53-fd5c-401a-ab70-0206cd537c58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_cea82096-5986-4335-9970-a1816714625f" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_54f43e53-fd5c-401a-ab70-0206cd537c58" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896fbc75-1b6d-4fa4-beb4-8514ef4aed11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_54f43e53-fd5c-401a-ab70-0206cd537c58" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896fbc75-1b6d-4fa4-beb4-8514ef4aed11" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_896fbc75-1b6d-4fa4-beb4-8514ef4aed11_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896fbc75-1b6d-4fa4-beb4-8514ef4aed11" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_896fbc75-1b6d-4fa4-beb4-8514ef4aed11_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_832a5ba5-c046-4b8e-a78e-6899f4d5f4db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_896fbc75-1b6d-4fa4-beb4-8514ef4aed11" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_832a5ba5-c046-4b8e-a78e-6899f4d5f4db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_d7977a86-7048-43ee-81ca-42af498e24ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_832a5ba5-c046-4b8e-a78e-6899f4d5f4db" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_d7977a86-7048-43ee-81ca-42af498e24ce" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_b19b607e-9be2-42ed-b34a-c40cfd0434c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_832a5ba5-c046-4b8e-a78e-6899f4d5f4db" xlink:to="loc_us-gaap_CustomerRelationshipsMember_b19b607e-9be2-42ed-b34a-c40cfd0434c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_9e721f84-160f-449f-86be-62fccb8f6387" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_832a5ba5-c046-4b8e-a78e-6899f4d5f4db" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_9e721f84-160f-449f-86be-62fccb8f6387" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ba6e5a83-9578-4c99-ba5e-6949c7af0adc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_54f43e53-fd5c-401a-ab70-0206cd537c58" xlink:to="loc_srt_RangeAxis_ba6e5a83-9578-4c99-ba5e-6949c7af0adc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ba6e5a83-9578-4c99-ba5e-6949c7af0adc_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ba6e5a83-9578-4c99-ba5e-6949c7af0adc" xlink:to="loc_srt_RangeMember_ba6e5a83-9578-4c99-ba5e-6949c7af0adc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3fccc201-e907-490b-964a-667524b90d2e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ba6e5a83-9578-4c99-ba5e-6949c7af0adc" xlink:to="loc_srt_RangeMember_3fccc201-e907-490b-964a-667524b90d2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_93806acc-011e-4854-b6e0-d93a948f9968" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3fccc201-e907-490b-964a-667524b90d2e" xlink:to="loc_srt_MinimumMember_93806acc-011e-4854-b6e0-d93a948f9968" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_0a7b6ec6-d147-4905-a691-ae2a3c448d9f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3fccc201-e907-490b-964a-667524b90d2e" xlink:to="loc_srt_MaximumMember_0a7b6ec6-d147-4905-a691-ae2a3c448d9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e4b32972-208b-4d08-8ea3-16de1c5c1a34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_cea82096-5986-4335-9970-a1816714625f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e4b32972-208b-4d08-8ea3-16de1c5c1a34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_030fefc9-7536-4eca-bb3f-522ddbcc52e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_cea82096-5986-4335-9970-a1816714625f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_030fefc9-7536-4eca-bb3f-522ddbcc52e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_bc83a4a6-5214-462f-b4e1-73ffc515f74b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_cea82096-5986-4335-9970-a1816714625f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_bc83a4a6-5214-462f-b4e1-73ffc515f74b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_377f0b2a-07df-4a7a-9505-034d05790938" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_cea82096-5986-4335-9970-a1816714625f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_377f0b2a-07df-4a7a-9505-034d05790938" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_80e6c1cd-dd70-49c4-8868-88c72ad5d032" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_651457a4-1b7f-4474-a680-0434bd0f48fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_80e6c1cd-dd70-49c4-8868-88c72ad5d032" xlink:to="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_651457a4-1b7f-4474-a680-0434bd0f48fa" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_28bf0c24-c7c2-488e-b3d8-066730daca9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_651457a4-1b7f-4474-a680-0434bd0f48fa" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_28bf0c24-c7c2-488e-b3d8-066730daca9e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_28bf0c24-c7c2-488e-b3d8-066730daca9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_28bf0c24-c7c2-488e-b3d8-066730daca9e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_28bf0c24-c7c2-488e-b3d8-066730daca9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_6aecd99f-fbab-4133-a483-40894dea400c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_28bf0c24-c7c2-488e-b3d8-066730daca9e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_6aecd99f-fbab-4133-a483-40894dea400c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_InProcessSoftwareDevelopmentCostsMember_3c655a25-3510-4d7d-baad-75cd05505d70" xlink:href="tls-20251231.xsd#tls_InProcessSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_6aecd99f-fbab-4133-a483-40894dea400c" xlink:to="loc_tls_InProcessSoftwareDevelopmentCostsMember_3c655a25-3510-4d7d-baad-75cd05505d70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_9b422296-2c55-475c-b682-0889520414de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_80e6c1cd-dd70-49c4-8868-88c72ad5d032" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_9b422296-2c55-475c-b682-0889520414de" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/INTANGIBLEASSETSNETNarrativeDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#INTANGIBLEASSETSNETNarrativeDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/INTANGIBLEASSETSNETNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_be8154a7-3fca-412c-98d3-2c58962d606e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0e23bec8-ae09-424f-9b03-26f16a973967" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_be8154a7-3fca-412c-98d3-2c58962d606e" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0e23bec8-ae09-424f-9b03-26f16a973967" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01e5e390-a1e1-450e-ad32-9b338c4fe590" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0e23bec8-ae09-424f-9b03-26f16a973967" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01e5e390-a1e1-450e-ad32-9b338c4fe590" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01e5e390-a1e1-450e-ad32-9b338c4fe590_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01e5e390-a1e1-450e-ad32-9b338c4fe590" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01e5e390-a1e1-450e-ad32-9b338c4fe590_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b8b2c8b8-272b-4436-b754-e3f387213961" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01e5e390-a1e1-450e-ad32-9b338c4fe590" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b8b2c8b8-272b-4436-b754-e3f387213961" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareDevelopmentMember_063bfecd-ef67-4652-b6e2-59c74ddfbe5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_b8b2c8b8-272b-4436-b754-e3f387213961" xlink:to="loc_us-gaap_SoftwareDevelopmentMember_063bfecd-ef67-4652-b6e2-59c74ddfbe5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_bef6076c-d2e9-4795-ad96-4a99e0bb1aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_be8154a7-3fca-412c-98d3-2c58962d606e" xlink:to="loc_us-gaap_AssetImpairmentCharges_bef6076c-d2e9-4795-ad96-4a99e0bb1aa7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_a4d52bbd-1ef5-41ad-b069-f1ac8fee6ad2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductionRelatedImpairmentsOrCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_be8154a7-3fca-412c-98d3-2c58962d606e" xlink:to="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_a4d52bbd-1ef5-41ad-b069-f1ac8fee6ad2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_42fe8389-7205-4329-9941-43bdfa42a97e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_be8154a7-3fca-412c-98d3-2c58962d606e" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_42fe8389-7205-4329-9941-43bdfa42a97e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/INTANGIBLEASSETSNETScheduleofAmortizationExpenseDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#INTANGIBLEASSETSNETScheduleofAmortizationExpenseDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/INTANGIBLEASSETSNETScheduleofAmortizationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b533c49-e187-466d-807f-98c0893eaa03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_8a552fd1-dbe4-4abe-a214-02967179faf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b533c49-e187-466d-807f-98c0893eaa03" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_8a552fd1-dbe4-4abe-a214-02967179faf0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_d9b7694d-d94f-478d-8b67-d7c070993a16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_8a552fd1-dbe4-4abe-a214-02967179faf0" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_d9b7694d-d94f-478d-8b67-d7c070993a16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d9b7694d-d94f-478d-8b67-d7c070993a16_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d9b7694d-d94f-478d-8b67-d7c070993a16" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d9b7694d-d94f-478d-8b67-d7c070993a16_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c071f50b-eb3d-42a3-917e-0e7d9bc98e51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d9b7694d-d94f-478d-8b67-d7c070993a16" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c071f50b-eb3d-42a3-917e-0e7d9bc98e51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ResearchAndDevelopmentNettingMember_16661d73-9ad7-46e4-9ea0-ae44b3b10ea7" xlink:href="tls-20251231.xsd#tls_ResearchAndDevelopmentNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c071f50b-eb3d-42a3-917e-0e7d9bc98e51" xlink:to="loc_tls_ResearchAndDevelopmentNettingMember_16661d73-9ad7-46e4-9ea0-ae44b3b10ea7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_0b6d1d4e-b3c3-47e5-ac27-c2aabe90fbbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_c071f50b-eb3d-42a3-917e-0e7d9bc98e51" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_0b6d1d4e-b3c3-47e5-ac27-c2aabe90fbbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldAmortization_14b45670-ff27-412b-babe-66d2e9257144" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSoldAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b533c49-e187-466d-807f-98c0893eaa03" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldAmortization_14b45670-ff27-412b-babe-66d2e9257144" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_e3fa2726-1d4d-499b-bef6-2b6da5e4fee7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b533c49-e187-466d-807f-98c0893eaa03" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_e3fa2726-1d4d-499b-bef6-2b6da5e4fee7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_IntangibleAssetsAmortizationExpense_506313d4-4130-4df1-a8cc-e6719cb85473" xlink:href="tls-20251231.xsd#tls_IntangibleAssetsAmortizationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_4b533c49-e187-466d-807f-98c0893eaa03" xlink:to="loc_tls_IntangibleAssetsAmortizationExpense_506313d4-4130-4df1-a8cc-e6719cb85473" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/REVOLVINGCREDITFACILITYDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#REVOLVINGCREDITFACILITYDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/REVOLVINGCREDITFACILITYDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_fd1d79ec-7cfd-4882-9f52-aa3c43e96dfe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_us-gaap_DebtInstrumentTable_fd1d79ec-7cfd-4882-9f52-aa3c43e96dfe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_93f7abf3-b9f7-430b-9ac5-c9addd4856d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fd1d79ec-7cfd-4882-9f52-aa3c43e96dfe" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_93f7abf3-b9f7-430b-9ac5-c9addd4856d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_93f7abf3-b9f7-430b-9ac5-c9addd4856d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_93f7abf3-b9f7-430b-9ac5-c9addd4856d4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_93f7abf3-b9f7-430b-9ac5-c9addd4856d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f151a0d7-b058-4308-aa03-ee0e38fac0f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_93f7abf3-b9f7-430b-9ac5-c9addd4856d4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f151a0d7-b058-4308-aa03-ee0e38fac0f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_bbe68334-c3ad-4bee-bc98-7f1980a774ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_f151a0d7-b058-4308-aa03-ee0e38fac0f6" xlink:to="loc_us-gaap_LineOfCreditMember_bbe68334-c3ad-4bee-bc98-7f1980a774ef" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_8a4e59b3-2729-4da0-818e-c97c0a574367" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fd1d79ec-7cfd-4882-9f52-aa3c43e96dfe" xlink:to="loc_us-gaap_DebtInstrumentAxis_8a4e59b3-2729-4da0-818e-c97c0a574367" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_8a4e59b3-2729-4da0-818e-c97c0a574367_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_8a4e59b3-2729-4da0-818e-c97c0a574367" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_8a4e59b3-2729-4da0-818e-c97c0a574367_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d565b657-c926-42c4-a6a3-e2181a4fd484" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_8a4e59b3-2729-4da0-818e-c97c0a574367" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d565b657-c926-42c4-a6a3-e2181a4fd484" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_CreditAgreementMember_a57545a6-1361-465b-8a5e-e340418954c4" xlink:href="tls-20251231.xsd#tls_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d565b657-c926-42c4-a6a3-e2181a4fd484" xlink:to="loc_tls_CreditAgreementMember_a57545a6-1361-465b-8a5e-e340418954c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecondAmendmentToCreditAgreementMember_019cd5d4-3e84-75a9-b1c5-5c9dd42dafcd" xlink:href="tls-20251231.xsd#tls_SecondAmendmentToCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d565b657-c926-42c4-a6a3-e2181a4fd484" xlink:to="loc_tls_SecondAmendmentToCreditAgreementMember_019cd5d4-3e84-75a9-b1c5-5c9dd42dafcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_c87bb42c-3258-4ad0-bfa2-68ea300c4963" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fd1d79ec-7cfd-4882-9f52-aa3c43e96dfe" xlink:to="loc_us-gaap_VariableRateAxis_c87bb42c-3258-4ad0-bfa2-68ea300c4963" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_c87bb42c-3258-4ad0-bfa2-68ea300c4963_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_c87bb42c-3258-4ad0-bfa2-68ea300c4963" xlink:to="loc_us-gaap_VariableRateDomain_c87bb42c-3258-4ad0-bfa2-68ea300c4963_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_c8ee374f-356c-43d7-8c7a-746d9a336296" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_c87bb42c-3258-4ad0-bfa2-68ea300c4963" xlink:to="loc_us-gaap_VariableRateDomain_c8ee374f-356c-43d7-8c7a-746d9a336296" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_AlternativeBaseRateMember_746304d4-18a0-458a-bf7c-12a8fa795789" xlink:href="tls-20251231.xsd#tls_AlternativeBaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_c8ee374f-356c-43d7-8c7a-746d9a336296" xlink:to="loc_tls_AlternativeBaseRateMember_746304d4-18a0-458a-bf7c-12a8fa795789" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_AdjustedDailySimpleSecuredOvernightFinancingRateSOFRMember_43a6d7d3-d226-4347-9d9c-1dd4043f2b98" xlink:href="tls-20251231.xsd#tls_AdjustedDailySimpleSecuredOvernightFinancingRateSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_c8ee374f-356c-43d7-8c7a-746d9a336296" xlink:to="loc_tls_AdjustedDailySimpleSecuredOvernightFinancingRateSOFRMember_43a6d7d3-d226-4347-9d9c-1dd4043f2b98" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_AdjustedTermSecuredOvernightFinancingRateSOFRMember_7e464cab-2072-4565-906e-facbe55dad29" xlink:href="tls-20251231.xsd#tls_AdjustedTermSecuredOvernightFinancingRateSOFRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_c8ee374f-356c-43d7-8c7a-746d9a336296" xlink:to="loc_tls_AdjustedTermSecuredOvernightFinancingRateSOFRMember_7e464cab-2072-4565-906e-facbe55dad29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_TermBenchmarkAndRFRLoansMember_019ce819-c7f3-7284-81e8-1bc8834044c9" xlink:href="tls-20251231.xsd#tls_TermBenchmarkAndRFRLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_c8ee374f-356c-43d7-8c7a-746d9a336296" xlink:to="loc_tls_TermBenchmarkAndRFRLoansMember_019ce819-c7f3-7284-81e8-1bc8834044c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_1e72b02a-2b05-4001-b4ff-a1bfd749c9b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_fd1d79ec-7cfd-4882-9f52-aa3c43e96dfe" xlink:to="loc_us-gaap_CreditFacilityAxis_1e72b02a-2b05-4001-b4ff-a1bfd749c9b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_1e72b02a-2b05-4001-b4ff-a1bfd749c9b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_1e72b02a-2b05-4001-b4ff-a1bfd749c9b4" xlink:to="loc_us-gaap_CreditFacilityDomain_1e72b02a-2b05-4001-b4ff-a1bfd749c9b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f7b4e9fc-036e-4758-ae22-7127f56b2733" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_1e72b02a-2b05-4001-b4ff-a1bfd749c9b4" xlink:to="loc_us-gaap_CreditFacilityDomain_f7b4e9fc-036e-4758-ae22-7127f56b2733" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_a047a138-3515-40d6-a3b1-af90f4b769e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f7b4e9fc-036e-4758-ae22-7127f56b2733" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_a047a138-3515-40d6-a3b1-af90f4b769e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_f84c4df6-d74e-4f28-8d6a-d2d9b459286c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f7b4e9fc-036e-4758-ae22-7127f56b2733" xlink:to="loc_us-gaap_LetterOfCreditMember_f84c4df6-d74e-4f28-8d6a-d2d9b459286c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_747fb500-e636-48d0-99c6-b8c2f123242f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_747fb500-e636-48d0-99c6-b8c2f123242f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_cf73e4b8-571a-4bb7-bf5c-7e19c3f04867" xlink:href="tls-20251231.xsd#tls_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_LineOfCreditFacilityAccordionFeatureHigherBorrowingCapacityOption_cf73e4b8-571a-4bb7-bf5c-7e19c3f04867" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_DebtInstrumentNumberOfVariableRates_c3593b2f-faa3-4b09-bad8-8acd20ba4d4b" xlink:href="tls-20251231.xsd#tls_DebtInstrumentNumberOfVariableRates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_DebtInstrumentNumberOfVariableRates_c3593b2f-faa3-4b09-bad8-8acd20ba4d4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_534c99f1-39a3-431d-b62f-896ce68e1c05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_534c99f1-39a3-431d-b62f-896ce68e1c05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_DebtInstrumentIncrementalIncreaseInInterestRateDueToDefault_c4675e57-2659-44c5-90bc-8f5a62790933" xlink:href="tls-20251231.xsd#tls_DebtInstrumentIncrementalIncreaseInInterestRateDueToDefault"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_DebtInstrumentIncrementalIncreaseInInterestRateDueToDefault_c4675e57-2659-44c5-90bc-8f5a62790933" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_DebtInstrumentPriorNoticePeriod_55e9964d-40a1-46b2-81e7-8af9b77866e2" xlink:href="tls-20251231.xsd#tls_DebtInstrumentPriorNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_DebtInstrumentPriorNoticePeriod_55e9964d-40a1-46b2-81e7-8af9b77866e2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_DebtInstrumentCovenantSeniorLeverageRatioMaximum_6fd10ce8-f4dd-4e9d-89f1-46f5fd0e2785" xlink:href="tls-20251231.xsd#tls_DebtInstrumentCovenantSeniorLeverageRatioMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_DebtInstrumentCovenantSeniorLeverageRatioMaximum_6fd10ce8-f4dd-4e9d-89f1-46f5fd0e2785" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ReceivablesExcludedFromCollateral_b5fd2361-468a-4267-a215-55badc47e870" xlink:href="tls-20251231.xsd#tls_ReceivablesExcludedFromCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_ReceivablesExcludedFromCollateral_b5fd2361-468a-4267-a215-55badc47e870" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019ba2fb-2ac0-713f-9ee9-49136b7b392f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_019ba2fb-2ac0-713f-9ee9-49136b7b392f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019ba2fd-2404-7e6b-840b-3729999def8d" xlink:href="tls-20251231.xsd#tls_LineOfCreditFacilityAccordionFeatureIncreaseLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_LineOfCreditFacilityAccordionFeatureIncreaseLimit_019ba2fd-2404-7e6b-840b-3729999def8d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_LineOfCreditFacilityDebtCovenantsDepositRequirementsAmount_019cdac0-6e39-730b-bc84-86d5c731607e" xlink:href="tls-20251231.xsd#tls_LineOfCreditFacilityDebtCovenantsDepositRequirementsAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_tls_LineOfCreditFacilityDebtCovenantsDepositRequirementsAmount_019cdac0-6e39-730b-bc84-86d5c731607e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cde6e-06a1-7187-90f1-016011e71159" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_199ee185-94b5-443f-b0bf-5f5cf402fbd0" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cde6e-06a1-7187-90f1-016011e71159" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/STOCKHOLDERSEQUITYScheduleofDetailsofChangesinAccumulatedOtherComprehensiveLossbyCategoryDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#STOCKHOLDERSEQUITYScheduleofDetailsofChangesinAccumulatedOtherComprehensiveLossbyCategoryDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/STOCKHOLDERSEQUITYScheduleofDetailsofChangesinAccumulatedOtherComprehensiveLossbyCategoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7debfa41-55a9-4956-83a3-614d24953841" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_254d9638-3947-42b1-b4c5-84a6108d32e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7debfa41-55a9-4956-83a3-614d24953841" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_254d9638-3947-42b1-b4c5-84a6108d32e6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_a7c5a2bb-cdcf-4117-970d-7508c4bf6590" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_254d9638-3947-42b1-b4c5-84a6108d32e6" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_a7c5a2bb-cdcf-4117-970d-7508c4bf6590" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_a7c5a2bb-cdcf-4117-970d-7508c4bf6590_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a7c5a2bb-cdcf-4117-970d-7508c4bf6590" xlink:to="loc_us-gaap_EquityComponentDomain_a7c5a2bb-cdcf-4117-970d-7508c4bf6590_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_676f130b-61bc-4c95-ad9d-e45d5251be15" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_a7c5a2bb-cdcf-4117-970d-7508c4bf6590" xlink:to="loc_us-gaap_EquityComponentDomain_676f130b-61bc-4c95-ad9d-e45d5251be15" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_58dba7ac-b243-425e-9c88-51c7ee7bb947" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_676f130b-61bc-4c95-ad9d-e45d5251be15" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_58dba7ac-b243-425e-9c88-51c7ee7bb947" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_f27a6b5f-01be-416b-ad68-0dc5afeaa2bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_58dba7ac-b243-425e-9c88-51c7ee7bb947" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_f27a6b5f-01be-416b-ad68-0dc5afeaa2bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_cb8ccbd3-a537-463f-93cb-9384ba72cc1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_58dba7ac-b243-425e-9c88-51c7ee7bb947" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_cb8ccbd3-a537-463f-93cb-9384ba72cc1d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_1553744e-e28e-418c-a8a3-b722b41721df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7debfa41-55a9-4956-83a3-614d24953841" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_1553744e-e28e-418c-a8a3-b722b41721df" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_56e064a3-58b8-4f6b-bf29-6aa6f932d996" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_1553744e-e28e-418c-a8a3-b722b41721df" xlink:to="loc_us-gaap_StockholdersEquity_56e064a3-58b8-4f6b-bf29-6aa6f932d996" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_a33b52a0-9537-46aa-a7c0-206a3ca50eff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_1553744e-e28e-418c-a8a3-b722b41721df" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_a33b52a0-9537-46aa-a7c0-206a3ca50eff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_7b1e2441-bb78-49b1-b378-87ae4c811686" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#STOCKBASEDCOMPENSATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/STOCKBASEDCOMPENSATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22a19c00-f1b7-4365-bc94-38ab67e9ec8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22a19c00-f1b7-4365-bc94-38ab67e9ec8d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019bdb56-2276-7564-adac-b9c502ad5bfe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22a19c00-f1b7-4365-bc94-38ab67e9ec8d" xlink:to="loc_us-gaap_PlanNameAxis_019bdb56-2276-7564-adac-b9c502ad5bfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019bdb56-2276-7564-adac-b9c502ad5bfe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019bdb56-2276-7564-adac-b9c502ad5bfe" xlink:to="loc_us-gaap_PlanNameDomain_019bdb56-2276-7564-adac-b9c502ad5bfe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019bdb56-2276-78fe-b26e-e3d29328ca3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019bdb56-2276-7564-adac-b9c502ad5bfe" xlink:to="loc_us-gaap_PlanNameDomain_019bdb56-2276-78fe-b26e-e3d29328ca3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_Two016OmnibusLongTermIncentivePlanMember_019bdb56-2276-77c2-9c50-41f6269017eb" xlink:href="tls-20251231.xsd#tls_Two016OmnibusLongTermIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019bdb56-2276-78fe-b26e-e3d29328ca3c" xlink:to="loc_tls_Two016OmnibusLongTermIncentivePlanMember_019bdb56-2276-77c2-9c50-41f6269017eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019bdb56-4625-7b7a-afa8-cfc3b9b28736" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22a19c00-f1b7-4365-bc94-38ab67e9ec8d" xlink:to="loc_us-gaap_AwardTypeAxis_019bdb56-4625-7b7a-afa8-cfc3b9b28736" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7b7a-afa8-cfc3b9b28736_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019bdb56-4625-7b7a-afa8-cfc3b9b28736" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7b7a-afa8-cfc3b9b28736_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7918-b98b-de8cc78e6916" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019bdb56-4625-7b7a-afa8-cfc3b9b28736" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7918-b98b-de8cc78e6916" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019bdb56-4625-7f4a-b801-fd83eefe6f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7918-b98b-de8cc78e6916" xlink:to="loc_us-gaap_PerformanceSharesMember_019bdb56-4625-7f4a-b801-fd83eefe6f9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ContingentPerformanceShares2027TargetsMember_019bdb56-4625-7b28-a1b4-51f28f863b60" xlink:href="tls-20251231.xsd#tls_ContingentPerformanceShares2027TargetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_019bdb56-4625-7f4a-b801-fd83eefe6f9b" xlink:to="loc_tls_ContingentPerformanceShares2027TargetsMember_019bdb56-4625-7b28-a1b4-51f28f863b60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ContingentPerformanceShares2025TargetsMember_019bdb56-4625-72cf-8b9a-ade4c99be9e1" xlink:href="tls-20251231.xsd#tls_ContingentPerformanceShares2025TargetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_019bdb56-4625-7f4a-b801-fd83eefe6f9b" xlink:to="loc_tls_ContingentPerformanceShares2025TargetsMember_019bdb56-4625-72cf-8b9a-ade4c99be9e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_TSRMarketConditionsPerformanceSharesMember_019ce830-bd2c-77b9-abc4-c0be30669327" xlink:href="tls-20251231.xsd#tls_TSRMarketConditionsPerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7918-b98b-de8cc78e6916" xlink:to="loc_tls_TSRMarketConditionsPerformanceSharesMember_019ce830-bd2c-77b9-abc4-c0be30669327" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_PerformanceSharesProbableOfAchievementAndRestrictedStockUnitsMember_019bdb56-8203-76f9-993f-e714c5f291a4" xlink:href="tls-20251231.xsd#tls_PerformanceSharesProbableOfAchievementAndRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7918-b98b-de8cc78e6916" xlink:to="loc_tls_PerformanceSharesProbableOfAchievementAndRestrictedStockUnitsMember_019bdb56-8203-76f9-993f-e714c5f291a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019bdb56-a24a-7ccc-98a1-a41ae39654cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019bdb56-4625-7918-b98b-de8cc78e6916" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019bdb56-a24a-7ccc-98a1-a41ae39654cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019bdb56-8203-7ae7-ad51-7c5407f1fbf4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22a19c00-f1b7-4365-bc94-38ab67e9ec8d" xlink:to="loc_srt_RangeAxis_019bdb56-8203-7ae7-ad51-7c5407f1fbf4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019bdb56-8203-7ae7-ad51-7c5407f1fbf4_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019bdb56-8203-7ae7-ad51-7c5407f1fbf4" xlink:to="loc_srt_RangeMember_019bdb56-8203-7ae7-ad51-7c5407f1fbf4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019bdb56-8203-783c-bf30-68cd2d843bd0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019bdb56-8203-7ae7-ad51-7c5407f1fbf4" xlink:to="loc_srt_RangeMember_019bdb56-8203-783c-bf30-68cd2d843bd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019bdb56-8203-75ce-b908-7e2154c59bb7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019bdb56-8203-783c-bf30-68cd2d843bd0" xlink:to="loc_srt_MinimumMember_019bdb56-8203-75ce-b908-7e2154c59bb7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019bdb56-8203-77c4-a295-e47b712a90c9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019bdb56-8203-783c-bf30-68cd2d843bd0" xlink:to="loc_srt_MaximumMember_019bdb56-8203-77c4-a295-e47b712a90c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_019cde94-cd22-7351-9247-b13a89722ff6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22a19c00-f1b7-4365-bc94-38ab67e9ec8d" xlink:to="loc_us-gaap_ValuationTechniqueAxis_019cde94-cd22-7351-9247-b13a89722ff6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019cde94-cd22-7351-9247-b13a89722ff6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019cde94-cd22-7351-9247-b13a89722ff6" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019cde94-cd22-7351-9247-b13a89722ff6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_019cde94-cd22-7614-a00b-a0a8ed5350fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_019cde94-cd22-7351-9247-b13a89722ff6" xlink:to="loc_us-gaap_ValuationTechniqueDomain_019cde94-cd22-7614-a00b-a0a8ed5350fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MonteCarloModelMember_019cde95-4756-72da-a364-5b0e37ba8e85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MonteCarloModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_019cde94-cd22-7614-a00b-a0a8ed5350fa" xlink:to="loc_us-gaap_MonteCarloModelMember_019cde95-4756-72da-a364-5b0e37ba8e85" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019bdb56-2276-77d0-aab4-2f2c328bc35e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019bdb56-2276-77d0-aab4-2f2c328bc35e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019bdb56-2276-78e7-bfb6-55e8b786698e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_019bdb56-2276-78e7-bfb6-55e8b786698e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_019bdb56-2276-7f3a-be3d-1a71da7fb165" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_019bdb56-2276-7f3a-be3d-1a71da7fb165" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost_019cc0c2-e732-7382-990a-dce8b5988a72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPlanModificationIncrementalCompensationCost_019cc0c2-e732-7382-990a-dce8b5988a72" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019bdb56-4625-7c8c-92b6-87a28c49b074" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019bdb56-4625-7c8c-92b6-87a28c49b074" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingConditionsStockPricesThresholdNumberOfConsecutiveDays_019bdb56-5ff3-7f89-b18b-90885f59ae1b" xlink:href="tls-20251231.xsd#tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingConditionsStockPricesThresholdNumberOfConsecutiveDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingConditionsStockPricesThresholdNumberOfConsecutiveDays_019bdb56-5ff3-7f89-b18b-90885f59ae1b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019bdb56-8203-7aa5-9524-4a6c42cb82b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019bdb56-8203-7aa5-9524-4a6c42cb82b5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPayoutPercentageOfSharesGranted_019bdb56-8203-7432-8853-fca189c1597f" xlink:href="tls-20251231.xsd#tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPayoutPercentageOfSharesGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardTargetPayoutPercentageOfSharesGranted_019bdb56-8203-7432-8853-fca189c1597f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019bdb56-8203-758a-a0eb-44c018d8c674" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019bdb56-8203-758a-a0eb-44c018d8c674" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019bdb56-8203-71fc-ac63-9d407930ed6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019bdb56-8203-71fc-ac63-9d407930ed6b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019bdb56-8203-76fa-98eb-09b2163f486d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019bdb56-8203-76fa-98eb-09b2163f486d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstandingExercisableAndVestedOrExpectedToVest_019bdb56-8203-7096-8bce-fb40a4213a2f" xlink:href="tls-20251231.xsd#tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstandingExercisableAndVestedOrExpectedToVest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_tls_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAggregateIntrinsicValueOutstandingExercisableAndVestedOrExpectedToVest_019bdb56-8203-7096-8bce-fb40a4213a2f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019bdb56-8203-78e0-acbb-08747395d3d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_019bdb56-8203-78e0-acbb-08747395d3d0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019bdb56-8203-7ad4-a0dd-edaf25f3bc47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_019bdb56-8203-7ad4-a0dd-edaf25f3bc47" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019bdb56-a24a-7823-8e22-8063c3ee240d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019bdb56-a24a-7823-8e22-8063c3ee240d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019bdb56-a24a-7299-92f7-8d1ca636614a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_019bdb56-a24a-7299-92f7-8d1ca636614a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019bdb56-a24a-7152-9ccf-3b6b00142dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_019bdb56-a24a-7152-9ccf-3b6b00142dd3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_019bdb56-a24a-782d-b308-110a4773c3e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedWeightedAverageGrantDateFairValue_019bdb56-a24a-782d-b308-110a4773c3e6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019bdb56-a24a-7238-8676-253a53e0c59c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019bdb56-a24a-7238-8676-253a53e0c59c" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019bdb56-a24a-77b4-a398-a99ad6d3bc1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019bdb56-2276-7ec1-b682-1d0ba8ce1976" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_019bdb56-a24a-77b4-a398-a99ad6d3bc1e" xlink:type="arc" order="19"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseIncurredDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseIncurredDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofStockBasedCompensationExpenseIncurredDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_06813a7f-323d-46b9-8976-d7bf3ff3faef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_fa665018-3ab5-45ac-8b34-40fb2905d919" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_06813a7f-323d-46b9-8976-d7bf3ff3faef" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_fa665018-3ab5-45ac-8b34-40fb2905d919" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_c64eb404-ecdf-4ca9-8213-7e180491b725" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_fa665018-3ab5-45ac-8b34-40fb2905d919" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_c64eb404-ecdf-4ca9-8213-7e180491b725" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_c64eb404-ecdf-4ca9-8213-7e180491b725_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_c64eb404-ecdf-4ca9-8213-7e180491b725" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_c64eb404-ecdf-4ca9-8213-7e180491b725_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_b25dc7a1-b517-4e96-83ca-2c6e6e5486af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_c64eb404-ecdf-4ca9-8213-7e180491b725" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_b25dc7a1-b517-4e96-83ca-2c6e6e5486af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_a5a5f515-a1dc-4055-879a-1cc4fa10afe9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_b25dc7a1-b517-4e96-83ca-2c6e6e5486af" xlink:to="loc_us-gaap_CostOfSalesMember_a5a5f515-a1dc-4055-879a-1cc4fa10afe9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_c2090aa2-0e6e-48c7-b056-6dbe61d5e09f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_b25dc7a1-b517-4e96-83ca-2c6e6e5486af" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_c2090aa2-0e6e-48c7-b056-6dbe61d5e09f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_27b898fd-5342-412b-af85-a37bb6f81bf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_b25dc7a1-b517-4e96-83ca-2c6e6e5486af" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_27b898fd-5342-412b-af85-a37bb6f81bf0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_6a6ef70c-630d-46ed-8718-3199a301433e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_fa665018-3ab5-45ac-8b34-40fb2905d919" xlink:to="loc_srt_ProductOrServiceAxis_6a6ef70c-630d-46ed-8718-3199a301433e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6a6ef70c-630d-46ed-8718-3199a301433e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_6a6ef70c-630d-46ed-8718-3199a301433e" xlink:to="loc_srt_ProductsAndServicesDomain_6a6ef70c-630d-46ed-8718-3199a301433e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6faac52c-33ef-4cf5-a7ab-377ccd22cef2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_6a6ef70c-630d-46ed-8718-3199a301433e" xlink:to="loc_srt_ProductsAndServicesDomain_6faac52c-33ef-4cf5-a7ab-377ccd22cef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_52f41f80-19a4-46d9-8b8b-9d1f3c6403ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_6faac52c-33ef-4cf5-a7ab-377ccd22cef2" xlink:to="loc_us-gaap_ServiceMember_52f41f80-19a4-46d9-8b8b-9d1f3c6403ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b615c9c3-1c24-458f-bfc2-e3d5f5982eeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_fa665018-3ab5-45ac-8b34-40fb2905d919" xlink:to="loc_us-gaap_AwardTypeAxis_b615c9c3-1c24-458f-bfc2-e3d5f5982eeb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b615c9c3-1c24-458f-bfc2-e3d5f5982eeb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b615c9c3-1c24-458f-bfc2-e3d5f5982eeb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b615c9c3-1c24-458f-bfc2-e3d5f5982eeb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6ae69873-d230-4e3b-8c0c-76fa27ad82d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b615c9c3-1c24-458f-bfc2-e3d5f5982eeb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6ae69873-d230-4e3b-8c0c-76fa27ad82d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_34393d69-f94e-40d1-9215-2f79ef628d63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6ae69873-d230-4e3b-8c0c-76fa27ad82d1" xlink:to="loc_us-gaap_EmployeeStockOptionMember_34393d69-f94e-40d1-9215-2f79ef628d63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_b5d671e3-819d-44df-9efd-4072a2340de4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_06813a7f-323d-46b9-8976-d7bf3ff3faef" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_b5d671e3-819d-44df-9efd-4072a2340de4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofRestrictedStockUnitActivityDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#STOCKBASEDCOMPENSATIONScheduleofRestrictedStockUnitActivityDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofRestrictedStockUnitActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4889564c-e34f-4b39-8b6d-acded8624b93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c4a1a7b1-c54e-4ef6-8892-7b7fcc50f47e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4889564c-e34f-4b39-8b6d-acded8624b93" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c4a1a7b1-c54e-4ef6-8892-7b7fcc50f47e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_8a4c615d-c439-4dfa-96fa-ba3bd474e2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c4a1a7b1-c54e-4ef6-8892-7b7fcc50f47e" xlink:to="loc_us-gaap_AwardTypeAxis_8a4c615d-c439-4dfa-96fa-ba3bd474e2a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8a4c615d-c439-4dfa-96fa-ba3bd474e2a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_8a4c615d-c439-4dfa-96fa-ba3bd474e2a3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_8a4c615d-c439-4dfa-96fa-ba3bd474e2a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08445318-dc69-4b44-96ca-8533524a0b01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_8a4c615d-c439-4dfa-96fa-ba3bd474e2a3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08445318-dc69-4b44-96ca-8533524a0b01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_ServiceBasedRSUAwardsMember_64fe5ba7-8088-4694-ba47-ce894392c687" xlink:href="tls-20251231.xsd#tls_ServiceBasedRSUAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08445318-dc69-4b44-96ca-8533524a0b01" xlink:to="loc_tls_ServiceBasedRSUAwardsMember_64fe5ba7-8088-4694-ba47-ce894392c687" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_9e7e5dd7-09aa-42ee-9b02-14ef62fdb029" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_08445318-dc69-4b44-96ca-8533524a0b01" xlink:to="loc_us-gaap_PerformanceSharesMember_9e7e5dd7-09aa-42ee-9b02-14ef62fdb029" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_db0c06e2-63de-4e72-9431-7629c41aa845" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4889564c-e34f-4b39-8b6d-acded8624b93" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_db0c06e2-63de-4e72-9431-7629c41aa845" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_67ba477b-01cc-43a0-ab59-28946266cc83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_db0c06e2-63de-4e72-9431-7629c41aa845" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_67ba477b-01cc-43a0-ab59-28946266cc83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_9f427251-1c10-4855-b2fb-1fe598d9b690" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_db0c06e2-63de-4e72-9431-7629c41aa845" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_9f427251-1c10-4855-b2fb-1fe598d9b690" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_27540897-c910-4a85-9ad4-64ed8b69caaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_db0c06e2-63de-4e72-9431-7629c41aa845" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_27540897-c910-4a85-9ad4-64ed8b69caaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_da2cb8fd-f889-4f74-bb66-5604569b5fd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_db0c06e2-63de-4e72-9431-7629c41aa845" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_da2cb8fd-f889-4f74-bb66-5604569b5fd9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_f09d9307-3f0e-4b2c-88fc-dc98b065f059" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4aaf6eb8-c486-42f1-90b0-0a463dc209f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4889564c-e34f-4b39-8b6d-acded8624b93" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4aaf6eb8-c486-42f1-90b0-0a463dc209f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_0ffff77a-9304-4834-a354-e545e93b4678" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4aaf6eb8-c486-42f1-90b0-0a463dc209f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_0ffff77a-9304-4834-a354-e545e93b4678" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0b34e1cd-7f81-4c12-a072-b85dc1edadbc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4aaf6eb8-c486-42f1-90b0-0a463dc209f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0b34e1cd-7f81-4c12-a072-b85dc1edadbc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_54860100-8367-4a6e-9b86-1571565d655c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4aaf6eb8-c486-42f1-90b0-0a463dc209f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_54860100-8367-4a6e-9b86-1571565d655c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_391f3e75-8d96-4fcc-9cac-dc33425ab004" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4aaf6eb8-c486-42f1-90b0-0a463dc209f6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_391f3e75-8d96-4fcc-9cac-dc33425ab004" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_e055b2b3-5aa2-47ae-bac6-0de3905c5446" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofStockPriceMarketConditionFairValueandAssumptionsDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#STOCKBASEDCOMPENSATIONScheduleofStockPriceMarketConditionFairValueandAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofStockPriceMarketConditionFairValueandAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d631a7cf-2ace-4d08-aa6a-c4ec860b8d1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d631a7cf-2ace-4d08-aa6a-c4ec860b8d1c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e709b037-33fe-40fe-aba3-cbb92f2df999" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d631a7cf-2ace-4d08-aa6a-c4ec860b8d1c" xlink:to="loc_us-gaap_AwardTypeAxis_e709b037-33fe-40fe-aba3-cbb92f2df999" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e709b037-33fe-40fe-aba3-cbb92f2df999_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e709b037-33fe-40fe-aba3-cbb92f2df999" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e709b037-33fe-40fe-aba3-cbb92f2df999_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_891ef9c8-9418-45b4-bf88-fb730bc320d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e709b037-33fe-40fe-aba3-cbb92f2df999" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_891ef9c8-9418-45b4-bf88-fb730bc320d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019ce822-8981-7bf7-9170-45865c6bd3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_891ef9c8-9418-45b4-bf88-fb730bc320d6" xlink:to="loc_us-gaap_PerformanceSharesMember_019ce822-8981-7bf7-9170-45865c6bd3bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019bdb5d-c2c4-77ba-b1ae-58220bf4f5e6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d631a7cf-2ace-4d08-aa6a-c4ec860b8d1c" xlink:to="loc_srt_RangeAxis_019bdb5d-c2c4-77ba-b1ae-58220bf4f5e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019bdb5d-c2c4-77ba-b1ae-58220bf4f5e6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019bdb5d-c2c4-77ba-b1ae-58220bf4f5e6" xlink:to="loc_srt_RangeMember_019bdb5d-c2c4-77ba-b1ae-58220bf4f5e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019bdb5d-c2c4-7327-ac7d-d5fd50fc11f8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019bdb5d-c2c4-77ba-b1ae-58220bf4f5e6" xlink:to="loc_srt_RangeMember_019bdb5d-c2c4-7327-ac7d-d5fd50fc11f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019bdb5d-e1ed-770f-8b69-7be24a599efc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019bdb5d-c2c4-7327-ac7d-d5fd50fc11f8" xlink:to="loc_srt_MinimumMember_019bdb5d-e1ed-770f-8b69-7be24a599efc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019bdb5e-19f1-7dd2-9559-43f67e6f382c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019bdb5d-c2c4-7327-ac7d-d5fd50fc11f8" xlink:to="loc_srt_MaximumMember_019bdb5e-19f1-7dd2-9559-43f67e6f382c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_3a9b4702-8ffa-403a-8bec-61848754ae2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_3a9b4702-8ffa-403a-8bec-61848754ae2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_cdbd0ff0-1517-4079-a90b-3861116f29f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_cdbd0ff0-1517-4079-a90b-3861116f29f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_daf98b5a-8e7d-46ee-9a3b-f0d7dc36a419" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_daf98b5a-8e7d-46ee-9a3b-f0d7dc36a419" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_6670b01d-046c-40ca-bdba-8e4156ccd259" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_6670b01d-046c-40ca-bdba-8e4156ccd259" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_35c669cf-c061-4468-a854-f8a3a0a3ae53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_aad2fb63-a965-4821-a767-f1f104cad991" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_35c669cf-c061-4468-a854-f8a3a0a3ae53" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofStockOptionActivityDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#STOCKBASEDCOMPENSATIONScheduleofStockOptionActivityDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/STOCKBASEDCOMPENSATIONScheduleofStockOptionActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8fc4f67f-2860-4846-abc2-865ea35d7bec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8fc4f67f-2860-4846-abc2-865ea35d7bec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_d5d74438-6967-4106-ab9e-fd11bed4ad6d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_8fc4f67f-2860-4846-abc2-865ea35d7bec" xlink:to="loc_srt_RangeAxis_d5d74438-6967-4106-ab9e-fd11bed4ad6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_d5d74438-6967-4106-ab9e-fd11bed4ad6d_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_d5d74438-6967-4106-ab9e-fd11bed4ad6d" xlink:to="loc_srt_RangeMember_d5d74438-6967-4106-ab9e-fd11bed4ad6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c1d63a29-79b7-475c-b33b-4e6116e74bad" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_d5d74438-6967-4106-ab9e-fd11bed4ad6d" xlink:to="loc_srt_RangeMember_c1d63a29-79b7-475c-b33b-4e6116e74bad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_368372a7-0963-4193-bdf9-6d4c13e02ea5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c1d63a29-79b7-475c-b33b-4e6116e74bad" xlink:to="loc_srt_MinimumMember_368372a7-0963-4193-bdf9-6d4c13e02ea5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_75bf7785-4043-4a2e-9ced-e1a033d1abd3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c1d63a29-79b7-475c-b33b-4e6116e74bad" xlink:to="loc_srt_MaximumMember_75bf7785-4043-4a2e-9ced-e1a033d1abd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5c93ed3a-52d6-4fdd-ac35-ca8b20d61e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5c93ed3a-52d6-4fdd-ac35-ca8b20d61e3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_b00cd4d2-0c4b-41ae-a69e-825be7c47690" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5c93ed3a-52d6-4fdd-ac35-ca8b20d61e3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_b00cd4d2-0c4b-41ae-a69e-825be7c47690" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_ceec8826-f861-47a3-b658-2591bde40038" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5c93ed3a-52d6-4fdd-ac35-ca8b20d61e3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_ceec8826-f861-47a3-b658-2591bde40038" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_c65dc2e8-9d96-405c-aa21-4fbaa69fe138" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5c93ed3a-52d6-4fdd-ac35-ca8b20d61e3d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_c65dc2e8-9d96-405c-aa21-4fbaa69fe138" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_80aeadea-1b1c-413c-b398-3996285d785a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_5c93ed3a-52d6-4fdd-ac35-ca8b20d61e3d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_80aeadea-1b1c-413c-b398-3996285d785a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_865e82b0-2f4e-4a39-82d9-865cc4660873" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_33438b49-5af4-423d-8d90-d6d397600870" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_33438b49-5af4-423d-8d90-d6d397600870" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_bd5aa4f4-72a9-412d-92e2-b7860924c98e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_bd5aa4f4-72a9-412d-92e2-b7860924c98e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2efd5066-1c54-4dd0-a0c2-590cb2738d91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_bd5aa4f4-72a9-412d-92e2-b7860924c98e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2efd5066-1c54-4dd0-a0c2-590cb2738d91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_c2a19d63-b317-4173-ab19-57fd6a59d5ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_bd5aa4f4-72a9-412d-92e2-b7860924c98e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_c2a19d63-b317-4173-ab19-57fd6a59d5ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_6843e9e0-7e8d-4d03-b9d6-04bcd20de811" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_bd5aa4f4-72a9-412d-92e2-b7860924c98e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_6843e9e0-7e8d-4d03-b9d6-04bcd20de811" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_531a6afd-033d-41b8-a91e-a3ffc3681744" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_bd5aa4f4-72a9-412d-92e2-b7860924c98e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_531a6afd-033d-41b8-a91e-a3ffc3681744" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_a2c1db23-c917-4930-9a5c-34fe61002e73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_ae126473-4e48-4e3a-9b98-187b477181dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_ae126473-4e48-4e3a-9b98-187b477181dc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_2d09b137-071a-49dd-b018-29235128f82d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_acc4d5dd-54d6-4e18-8489-550cff6f31e3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_2d09b137-071a-49dd-b018-29235128f82d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_88d45920-e489-4682-9db0-6863dce16603" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_2d09b137-071a-49dd-b018-29235128f82d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_88d45920-e489-4682-9db0-6863dce16603" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_ff40357f-8db0-404c-b716-75be57d6b8ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_2d09b137-071a-49dd-b018-29235128f82d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_ff40357f-8db0-404c-b716-75be57d6b8ac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_3314cabc-378c-49ae-b141-61dc38945675" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_2d09b137-071a-49dd-b018-29235128f82d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue_3314cabc-378c-49ae-b141-61dc38945675" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_add74224-2df2-4553-9d95-3de3631f977e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_2d09b137-071a-49dd-b018-29235128f82d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_add74224-2df2-4553-9d95-3de3631f977e" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/INCOMETAXESScheduleofValuationAllowanceActivityDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#INCOMETAXESScheduleofValuationAllowanceActivityDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/INCOMETAXESScheduleofValuationAllowanceActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_1bae5b05-19fd-459c-a8de-8697378953bd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ValuationAndQualifyingAccountsDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_703d4fcd-8f2f-4448-89c4-42106ac9c0b2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ValuationAndQualifyingAccountsDisclosureTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_1bae5b05-19fd-459c-a8de-8697378953bd" xlink:to="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_703d4fcd-8f2f-4448-89c4-42106ac9c0b2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_69ecc5b4-7124-4474-8d5e-0cd33c0c085f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureTable_703d4fcd-8f2f-4448-89c4-42106ac9c0b2" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_69ecc5b4-7124-4474-8d5e-0cd33c0c085f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_69ecc5b4-7124-4474-8d5e-0cd33c0c085f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_69ecc5b4-7124-4474-8d5e-0cd33c0c085f" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_69ecc5b4-7124-4474-8d5e-0cd33c0c085f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesDomain_2a3abae1-e707-4512-a544-f073d0325985" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesTypeAxis_69ecc5b4-7124-4474-8d5e-0cd33c0c085f" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesDomain_2a3abae1-e707-4512-a544-f073d0325985" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember_50033699-c3b8-46f3-8be4-d1e2e5ccf406" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationAllowancesAndReservesDomain_2a3abae1-e707-4512-a544-f073d0325985" xlink:to="loc_us-gaap_ValuationAllowanceOfDeferredTaxAssetsMember_50033699-c3b8-46f3-8be4-d1e2e5ccf406" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_ec1ca28d-f665-4779-822e-102338905499" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MovementInValuationAllowancesAndReservesRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ValuationAndQualifyingAccountsDisclosureLineItems_1bae5b05-19fd-459c-a8de-8697378953bd" xlink:to="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_ec1ca28d-f665-4779-822e-102338905499" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_b977c60a-8c42-4d22-8ee8-9e4b39073e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_ec1ca28d-f665-4779-822e-102338905499" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesBalance_b977c60a-8c42-4d22-8ee8-9e4b39073e2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesAdjustments_02aa689f-b994-4a19-90f9-23c99efe0d67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MovementInValuationAllowancesAndReservesRollForward_ec1ca28d-f665-4779-822e-102338905499" xlink:to="loc_us-gaap_ValuationAllowancesAndReservesAdjustments_02aa689f-b994-4a19-90f9-23c99efe0d67" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationAllowancesAndReservesBalance_b07e6247-3104-4aa5-97f4-1bf506010b42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationAllowancesAndReservesBalance"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/INCOMETAXESScheduleofComponentsofIncomeTaxesPaidDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#INCOMETAXESScheduleofComponentsofIncomeTaxesPaidDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/INCOMETAXESScheduleofComponentsofIncomeTaxesPaidDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019cd455-9160-7b6d-8a08-ca77370c0d57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019cd455-9160-7562-90b6-23cc97b81934" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidByIndividualJurisdictionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019cd455-9160-7b6d-8a08-ca77370c0d57" xlink:to="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019cd455-9160-7562-90b6-23cc97b81934" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019cd455-9160-74ff-be59-003adbe6796a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionTable_019cd455-9160-7562-90b6-23cc97b81934" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019cd455-9160-74ff-be59-003adbe6796a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019cd455-9160-74ff-be59-003adbe6796a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019cd455-9160-74ff-be59-003adbe6796a" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019cd455-9160-74ff-be59-003adbe6796a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019cd455-9160-782f-a350-0ff349d6c3e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019cd455-9160-74ff-be59-003adbe6796a" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019cd455-9160-782f-a350-0ff349d6c3e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_TX_019cd455-9160-7d8a-93c5-b02201fc75dc" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_TX"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019cd455-9160-782f-a350-0ff349d6c3e5" xlink:to="loc_stpr_TX_019cd455-9160-7d8a-93c5-b02201fc75dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_PH_019cd455-9160-7f46-a8e7-082b9bc3e55d" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_PH"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019cd455-9160-782f-a350-0ff349d6c3e5" xlink:to="loc_country_PH_019cd455-9160-7f46-a8e7-082b9bc3e55d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_019cd455-9160-7b3a-840e-7a18b7715b3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019cd455-9160-7b6d-8a08-ca77370c0d57" xlink:to="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_019cd455-9160-7b3a-840e-7a18b7715b3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidForeignAfterRefundReceived_019cd455-9160-778f-a6af-b3697d4f06ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidForeignAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxPaidByIndividualJurisdictionLineItems_019cd455-9160-7b6d-8a08-ca77370c0d57" xlink:to="loc_us-gaap_IncomeTaxPaidForeignAfterRefundReceived_019cd455-9160-778f-a6af-b3697d4f06ab" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/LOSSPERSHAREDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#LOSSPERSHAREDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/LOSSPERSHAREDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e9e941d5-f644-4b97-a63b-07387b016cc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5f713177-5b61-4406-8afb-2d3a37302469" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e9e941d5-f644-4b97-a63b-07387b016cc5" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5f713177-5b61-4406-8afb-2d3a37302469" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5607109c-c453-4ff0-a1a5-bc22a869ba80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_5f713177-5b61-4406-8afb-2d3a37302469" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5607109c-c453-4ff0-a1a5-bc22a869ba80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5607109c-c453-4ff0-a1a5-bc22a869ba80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5607109c-c453-4ff0-a1a5-bc22a869ba80" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5607109c-c453-4ff0-a1a5-bc22a869ba80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d8a2a905-4d9b-4264-8b8d-96cb94d8e938" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5607109c-c453-4ff0-a1a5-bc22a869ba80" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d8a2a905-4d9b-4264-8b8d-96cb94d8e938" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_21df15a1-516b-40a1-a522-1fab743591d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d8a2a905-4d9b-4264-8b8d-96cb94d8e938" xlink:to="loc_us-gaap_StockCompensationPlanMember_21df15a1-516b-40a1-a522-1fab743591d4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_868968a1-71ee-4d15-b30f-9279782c5023" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e9e941d5-f644-4b97-a63b-07387b016cc5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_868968a1-71ee-4d15-b30f-9279782c5023" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_IncrementalCommonSharesExcludedFromTheDilutiveEffect_7cdbe3c1-b01a-4acd-81c0-977148ce6a00" xlink:href="tls-20251231.xsd#tls_IncrementalCommonSharesExcludedFromTheDilutiveEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e9e941d5-f644-4b97-a63b-07387b016cc5" xlink:to="loc_tls_IncrementalCommonSharesExcludedFromTheDilutiveEffect_7cdbe3c1-b01a-4acd-81c0-977148ce6a00" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/SEGMENTINFORMATIONScheduleofSegmentReportingInformationbySegmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingRevenueReconcilingItemLineItems_be75aa6e-05c2-45d6-8841-2731ed6ab7c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingRevenueReconcilingItemLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTable_54bb6be2-d87a-4cbe-bdf5-32e72dd95a31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingRevenueReconcilingItemLineItems_be75aa6e-05c2-45d6-8841-2731ed6ab7c8" xlink:to="loc_us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTable_54bb6be2-d87a-4cbe-bdf5-32e72dd95a31" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_5383adee-8679-4506-83d9-d2f1c08781b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfRevenueFromSegmentsToConsolidatedTable_54bb6be2-d87a-4cbe-bdf5-32e72dd95a31" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_5383adee-8679-4506-83d9-d2f1c08781b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_5383adee-8679-4506-83d9-d2f1c08781b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5383adee-8679-4506-83d9-d2f1c08781b0" xlink:to="loc_us-gaap_SegmentDomain_5383adee-8679-4506-83d9-d2f1c08781b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_bbc7d114-164f-4bc4-8b75-da9ca596ed6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_5383adee-8679-4506-83d9-d2f1c08781b0" xlink:to="loc_us-gaap_SegmentDomain_bbc7d114-164f-4bc4-8b75-da9ca596ed6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecuritySolutionsSegmentMember_0828a44f-4adf-4ee9-9a6d-52bedadf0499" xlink:href="tls-20251231.xsd#tls_SecuritySolutionsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_bbc7d114-164f-4bc4-8b75-da9ca596ed6c" xlink:to="loc_tls_SecuritySolutionsSegmentMember_0828a44f-4adf-4ee9-9a6d-52bedadf0499" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_SecureNetworksSegmentMember_49051aa2-a339-4aec-91ff-57b7aa6fc7a4" xlink:href="tls-20251231.xsd#tls_SecureNetworksSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_bbc7d114-164f-4bc4-8b75-da9ca596ed6c" xlink:to="loc_tls_SecureNetworksSegmentMember_49051aa2-a339-4aec-91ff-57b7aa6fc7a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_d5170f66-7fe4-41d9-a6af-a07dd3cbbbec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingRevenueReconcilingItemLineItems_be75aa6e-05c2-45d6-8841-2731ed6ab7c8" xlink:to="loc_us-gaap_RevenuesAbstract_d5170f66-7fe4-41d9-a6af-a07dd3cbbbec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_70819b3c-b135-42cb-b7bc-a57c16d3fee4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_d5170f66-7fe4-41d9-a6af-a07dd3cbbbec" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_70819b3c-b135-42cb-b7bc-a57c16d3fee4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductionRelatedImpairmentsOrChargesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingRevenueReconcilingItemLineItems_be75aa6e-05c2-45d6-8841-2731ed6ab7c8" xlink:to="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_7e01bf3d-3af9-4d54-8642-56877a9d426a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductionRelatedImpairmentsOrCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:to="loc_us-gaap_ProductionRelatedImpairmentsOrCharges_7e01bf3d-3af9-4d54-8642-56877a9d426a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_3289e2c1-0905-4d79-bc98-e4845c5c9a0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSoldDepreciationAndAmortization_3289e2c1-0905-4d79-bc98-e4845c5c9a0d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_CostShareBasedPaymentArrangementExpense_99cdf85d-a1f2-4b50-a833-380b0a77972d" xlink:href="tls-20251231.xsd#tls_CostShareBasedPaymentArrangementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:to="loc_tls_CostShareBasedPaymentArrangementExpense_99cdf85d-a1f2-4b50-a833-380b0a77972d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_70d3ea51-64a4-4f1b-8694-a1ad426e8b32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_70d3ea51-64a4-4f1b-8694-a1ad426e8b32" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_ec989f06-1916-4a89-8a38-a6fc5b725315" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_ec989f06-1916-4a89-8a38-a6fc5b725315" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossProfit_d8ae5690-27cc-46ba-8aa0-c05427ebff67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GrossProfit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductionRelatedImpairmentsOrChargesAbstract_5716a5bb-c3b7-4988-8fd7-2e7d6b762383" xlink:to="loc_us-gaap_GrossProfit_d8ae5690-27cc-46ba-8aa0-c05427ebff67" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingRevenueReconcilingItemLineItems_be75aa6e-05c2-45d6-8841-2731ed6ab7c8" xlink:to="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_b52eebd7-d99b-47e7-8003-6760f53a1514" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_b52eebd7-d99b-47e7-8003-6760f53a1514" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_ca175bfb-f069-4513-8421-3369e36a28f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_ca175bfb-f069-4513-8421-3369e36a28f7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019bdb29-8e17-7038-b1a0-069865477393" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019bdb29-8e17-7038-b1a0-069865477393" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_e4f83372-b49f-4754-8e6c-7e538223abf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfIntangibleAssetsFinitelived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_ImpairmentOfIntangibleAssetsFinitelived_e4f83372-b49f-4754-8e6c-7e538223abf4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpenses_47156df3-c7a2-4446-a8aa-e26f563016b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_OperatingExpenses_47156df3-c7a2-4446-a8aa-e26f563016b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_df3e5270-ab60-4b5c-b86e-413379fefb81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_OperatingIncomeLoss_df3e5270-ab60-4b5c-b86e-413379fefb81" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_e9597b94-f767-450d-a084-bb3f7166d0f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_e9597b94-f767-450d-a084-bb3f7166d0f1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_88dc7c1e-0677-45bd-bc1b-385087f7018b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_InterestExpenseNonoperating_88dc7c1e-0677-45bd-bc1b-385087f7018b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_11d26603-3b4f-4f7e-9522-dd286f672a2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_11d26603-3b4f-4f7e-9522-dd286f672a2a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_afd2331f-9666-44c6-9057-4a634157176f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_afd2331f-9666-44c6-9057-4a634157176f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_3c3956a0-b00f-4d8d-a65c-551ccbd013ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_defffd33-76db-4aab-918e-5c807774bf80" xlink:to="loc_us-gaap_NetIncomeLoss_3c3956a0-b00f-4d8d-a65c-551ccbd013ce" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://telos.com/role/COMMITMENTSCONTINGENCIESANDSUBSEQUENTEVENTSDetails" xlink:type="simple" xlink:href="tls-20251231.xsd#COMMITMENTSCONTINGENCIESANDSUBSEQUENTEVENTSDetails"/>
  <link:definitionLink xlink:role="http://telos.com/role/COMMITMENTSCONTINGENCIESANDSUBSEQUENTEVENTSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_019c9caf-226c-7483-9188-ecfd5300e1e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_019c9caf-226c-703e-b1e8-9c68cdc903e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019c9caf-226c-7483-9188-ecfd5300e1e3" xlink:to="loc_us-gaap_OtherCommitmentsTable_019c9caf-226c-703e-b1e8-9c68cdc903e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019c9cb0-fe81-7167-a398-d9c9fc7b7e82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019c9caf-226c-703e-b1e8-9c68cdc903e2" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019c9cb0-fe81-7167-a398-d9c9fc7b7e82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9cb0-fe81-7167-a398-d9c9fc7b7e82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9cb0-fe81-7167-a398-d9c9fc7b7e82" xlink:to="loc_us-gaap_EquityComponentDomain_019c9cb0-fe81-7167-a398-d9c9fc7b7e82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019c9cb0-fe81-790f-8e7f-b003a04891c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019c9cb0-fe81-7167-a398-d9c9fc7b7e82" xlink:to="loc_us-gaap_EquityComponentDomain_019c9cb0-fe81-790f-8e7f-b003a04891c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019c9cb1-20c1-79b7-9968-03567a7db10a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019c9cb0-fe81-790f-8e7f-b003a04891c2" xlink:to="loc_us-gaap_CommonStockMember_019c9cb1-20c1-79b7-9968-03567a7db10a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019cb134-b7ae-7cb2-b0fd-965282afb640" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_019c9caf-226c-703e-b1e8-9c68cdc903e2" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019cb134-b7ae-7cb2-b0fd-965282afb640" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019cb134-b7ae-7cb2-b0fd-965282afb640_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019cb134-b7ae-7cb2-b0fd-965282afb640" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019cb134-b7ae-7cb2-b0fd-965282afb640_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019cb134-b7ae-78a0-9bc5-14c74b07c137" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019cb134-b7ae-7cb2-b0fd-965282afb640" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019cb134-b7ae-78a0-9bc5-14c74b07c137" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019cb134-dfaa-76c9-af1a-f5a07c06dd2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019cb134-b7ae-78a0-9bc5-14c74b07c137" xlink:to="loc_us-gaap_SubsequentEventMember_019cb134-dfaa-76c9-af1a-f5a07c06dd2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_tls_StockRepurchaseProgramAdditionalAuthorizedAmount_019cde8c-29f7-7bf4-98ce-9781a923c79a" xlink:href="tls-20251231.xsd#tls_StockRepurchaseProgramAdditionalAuthorizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019c9caf-226c-7483-9188-ecfd5300e1e3" xlink:to="loc_tls_StockRepurchaseProgramAdditionalAuthorizedAmount_019cde8c-29f7-7bf4-98ce-9781a923c79a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019cde9a-a2a5-720a-8be9-cf7d8adb428a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_019c9caf-226c-7483-9188-ecfd5300e1e3" xlink:to="loc_us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1_019cde9a-a2a5-720a-8be9-cf7d8adb428a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense" xlink:type="arc" order="691"/>
  </link:definitionLink>
</link:linkbase>
