What is a protocol?
A protocol is a standard set of rules that governs how computers communicate with each other. Protocols describe both the format that a message must take and the way in which messages are exchanged between computers.
Different types of computers are able to communicate with each other - in spite of their differences - when they agree to use a protocol that offers a standard format and method for communication. Some of the protocols used on the Internet are TCP/IP, SMTP, FTP, HTTP, and NNTP.