Effective communication depends on the use of a common language. This is true for humans and other animals as well as for computers. When a set of common behaviors is used with a common language, a protocol is being used. The first definition of a protocol, according to the New Oxford American Dictionary, is
The official procedure or system of rules governing affairs of state or diplomatic occasions.
We engage in many protocols every day: asking and responding to questions, negotiating business transactions, working collaboratively, and so on. Computers also engage in a variety of protocols. A collection of related protocols is called a protocol suite. The design that specifies how various protocols of a protocol suite relate ...