third partyˌthird ˈparty noun (plural third parties) [countableC]1LAW someone who is not one of the two main people or organizations involved in an agreement or legal caseThe preference tests were conducted by an independent third party.
2INSURANCE in an insurance contract, someone who is not the insurer or the insured person, but who will get money if the insured person causes them loss or injuryThe insurance only covers loss or injury to a third party.