1. Law - contract - legal proceedings - agreements - other arrangements - noun.
A person or other entity not directly involved in a contract, transaction or legal proceedings.
2. Law - contract - legal proceedings - agreements - other arrangements - adjective.
Relating to such a person or entity.
Often written third-party.
For example, KY3P refers to knowledge and understanding of third-party risk in relation to transactions.
Third parties would include, for example, suppliers as well as customers.