协议(xié yì) - agreement, pact, protocol in Mandarin

协议 (xié yì) is the word for a negotiated agreement between two parties: business contracts, peace deals, divorce settlements, and in computing the network protocols that let machines agree how to talk.

The verbs that go with it are worth learning as a set: 签协议 (sign one), 达成协议 (reach one), 违反协议 (break one). Its measure word is 份 for the document and 项 for the deal itself.

The near neighbour is 合同, a contract. 合同 is the legally binding paperwork with obligations on both sides; 协议 is broader and can be a looser understanding, which is why 口头协议, a verbal agreement, is normal Chinese while 口头合同 is not.