The rules governing the exchange of information between devices on a data link.
For computers engaged in telecommunications, the protocol must be the same for both devices when receiving and transmitting information. A communications program can be used to ensure the baud rate, duplex, parity, data bits, and stop bits are correctly set.
A standard (language and a set of rules) to allow computers to interact in a standard way. Examples are IP, FTP, and HTTP.
Keywords:  medium, agreement, users
an agreement between the users of a communication medium about how the medium is to be used