protocol

A set of semantic and syntactic rules that determines the behavior of functional units in achieving communication. (I) Protocols can determine low-level details of machine-to-machine interfaces, such as the order in which bits from a byte are sent; they can also determine high-level exchanges between application programs, such as file transfer.
A set of rules governing the operation of functional units of a communication system that must be followed if communication is to take place.
In Open Systems Interconnection architecture, a set of semantic and syntactic rules that determine the behavior of entities in the same layer in performing communication functions. (T)