A communication protocol is simply an agreement by two or more parties about what rules will be followed when communications between or among the parties take place. Humans use (mostly
informal) protocols all the time when communicating. Think, for example, of making a simple telephone call: A caller dials the number, the phone at the other end rings, a person picks up the receiver and says, “Hello”, the caller identifies himself or herself and states the purpose of the call,
the recipient responds, there are perhaps more exchanges, after which the caller says, “Thank you. Goodbye.” Finally, the caller hangs up, and the recipient then hangs up as well. That’s a communication protocol in action.
A web protocol is, similarly, an agreed-upon set of rules and data formats to be used when two or more computers or other devices, or application programs running on those machines, wish to communicate across the Internet, usually but not always on behalf of human users. In any given communication it is likely that there will be several different protocols involved.