In networking, a protocol is the specification of a set of rules for a particular type of communication. Different protocols often describe different aspects of a single communication; taken together, these form a protocol stack. The terms "protocol" and "protocol stack" also refer to the software that implements a protocol.
See also: network protocol
In international law and international relations, a protocol is a treaty or international agreement that supplements a previous treaty or international agreement. A protocol can amend the previous treaty, or add additional provisions. Parties to the earlier agreement are not required to adopt the protocol; sometimes this is made clearer by calling it an 'optional protocol', especially where many parties to the first agreement do not support the protocol.
Some examples: the United Nations Framework Convention on Climate Change (UNFCC) established a framework for the development of binding greenhouse gas emission limits, while the Kyoto Protocol contained the limits later agreed upon.