According dictionaries there a few definitions of a word protocol (isn’t there always a few) but in computer science and engineering the most important one is that a protocol is, according The American Heritage® Dictionary, “a standard procedure for regulating data transmission between computers”. The word originated in old Greek from words “prôto” meaning “proto” and “kollêma” meaning “sheets of a papyrus glued together” (“kolla” = “glue”).
Protocol is a standard rule or set of rules that define a communication between different systems that use different software. A protocol is a necessity in order to transmit data between otherwise completely different systems, i.e. a computer (and therefore a person) from India and a computer from United States. There are many communication protocols out there, each of them governing a specific technology and how its data transfer works in sense of sending packets, compressing data, visualizing it on screens, etc. Some more “famous” data protocols are TCP, HTTP and WiFi or Transmission Control Protocol used for data transmission over a network, Hypertext Transfer Protocol used for transmitting and displaying information as web pages on browsers and Wireless Fidelity used for wireless communication.