1 [U] (formal 正式) a system of fixed rules and formal behaviour used at official meetings, usually between governments 外交礼仪（通常指政府间的）；礼节: a breach of protocol 外交礼仪的破坏the protocol of diplomatic visits 外交访问的礼遇

2 [C] (technical术语) the first or original version of a written agreement, especially one between countries; an extra part added to a written agreement 议定书，协议书（尤指国家间的）；（协议书的）补充条款: the first Geneva Protocol 第一个日内瓦议定书It is set out in a legally binding protocol which forms part of the treaty. 这在有法律效力的协议书中已经阐明，该协议书是条约的组成部份。

3 [C] (computing计算机技术) a set of rules that control the way information is sent between computers （计算机之间发送信息的）规程

4 [C] (technical术语) a plan for carrying out a scientific experiment or medical treatment 科学试验；治疗方案