What is the meaning of Third-party?

Of or relating to a third party.

1. Of products, created or published by an independent publisher or manufacturer or its internal development teams, as opposed to first-party and second-party.

   Of products, created or published by an independent publisher or manufacturer or its internal development teams, as opposed to first-party and second-party.

   To intervene in a fight between two players or teams, often allowing one to easily defeat both (sometimes seen as unfair).

   Source: wiktionary.org