first-party

Short definition from Wiktionary

Adjective

1. 1
   Of or relating to someone (a first party) directly involved in a given transaction, such as a buyer or seller.
2. 2
   Of or relating to the plaintiff in a lawsuit.
3. 3
   Of products, created or published by the company responsible for the platform on which it is released (or its internal developers), as opposed to third-party.

Noun

1. 1
   An individual or entity directly involved in a given transaction, such as a buyer or seller.
2. 2
   The plaintiff in a lawsuit.