This is defination of protocol:

When computers communicate with each other, there needs to be a common set of rules and instructions that each computer follows. A specific set of communication rules is called a protocol. Because of the many ways computers can communicate with each other, there are many different protocols -- too many for the average person to remember. Some examples of these different protocols include PPP, TCP/IP, SLIP, HTTP, and FTP. Can you guess what the last "P" in each acronym stands for? If you guessed "protocol," send yourself a congratulations e-mail.

A protocol is a set of rules that govern all aspects of information communication.