Sometimes referred to as an access method, a protocol is a standard used to define a method of exchanging data over a computer network, such as local area network, Internet, Intranet, etc. Each protocol has its own method of how data is formatted when sent and what to do with it once received, how that data is compressed, or how to check for errors in the data.
Likely the most important protocol is TCP/IP (Transmission Control Protocol/Internet Protocol) which is used to govern the communications of every computer connected to the internet. HTTP (HyperText Transfer Protocol), which is a used to transmit data over the world wide web (Internet), is "carried" by TCP/IP. Below is a list of the various protocols currently listed in the Computer Hope dictionary.