someone other than the parties directly involved in the action or transaction; outsider with no legal interest in the matter.
someone other than the maker of a machine and the end user. For example, third-party software is software that does not come from the manufacturer of the computer, nor is it developed by the user. Most software today is third-party software.
individual other than the insured or insurer who has incurred a loss or is entitled to receive a benefit payment as the result of the acts or omissions of the insured.