A protocol is a rule or set of rules for correspondence or interaction. The rule defines two necessary aspects of an interaction:
- How the interaction is to be conducted
- The form of the information that is exchanged during the interaction
If you consider all the protocols we are exposed to, these two little aspects of protocols cover every situation. For example:
- In police dramas, it is frequently claimed that being suspicious of family members of murdered victims, and questioning them is engaged as a matter of protocol - or procedure.
- When children misbehave in a schoolyard, a protocol is invoked to deal with the situation.
- When you plug a memory stick into your computer, a protocol governs how the computer reacts and how the stick is constructed such that the computer can deal with it.
In each of these cases, how the interaction proceeds and the form of the information that is exchanged is more or less governed by rules.
In the case of the stunning array of interactions that can transpire in open society, we don't necessarily regard them all as governed by protocols. We speak of culture and convention. I think protocol.
In the case of the stunning array of interactions that can transpire among computer parts and on the internet, we see protocols everywhere. There is the Internet Protocol (IP) and the hyper text transfer protocol (http), which we all hear about but know nothing about. In this technically-oriented business, we use the word protocol to define the nature of the rules being accorded, because not all rules are about protocols.
If you have an hour to kill, have a look at Wikipedia's story of protocols.