Hypertext Transfer Protocol (HTTP)

HTTP is used by the World Wide Web. The well-known port number associated with HTTP is 80. HTTP clients are called Web browsers; on UNIX, the most common browsers are Netscape Navigator (which runs under X) and a text-only browser called Lynx. Web server processes are widely available; an extremely common, useful, free Web server is Apache (which runs as a process called httpd or apache).

The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems.
HTTP is the foundation of data communication for the World Wide Web.
Hypertext is a multi-linear set of objects, building a network by using logical links (the so-called hyperlinks) between the nodes (e.g. text or words). HTTP is the protocol to exchange or transfer hypertext.
The standards development of HTTP was coordinated by the Internet Engineering Task Force (IETF) and the World Wide Web Consortium (W3C), culminating in the publication of a series of Requests for Comments (RFCs), most notably RFC 2616 (June 1999), which defines HTTP/1.1, the version of HTTP in common use.

The term Hypertext that we take for granted today was coined around 1963 and first published in 1965 by Ted Nelson, a software designer and visionary. He proposed the concept of hypertext to mean:

a body of written or pictorial material interconnected in such a complex way that it could not conveniently be presented or represented on paper. It may contain summaries, or maps of its contents and their interrelations; it may contain annotations, additions and footnotes from scholars who have examined it.

Nelson wanted to create a "docuverse" where information was interlinked and never deleted and easily available to all. He built on Bush's ideas and in the 1970s created a prototype implementation of a hypertext system with his project Xanadu. It was unfortunately never completed, but provided the shoulders to stand on for those to come.
HTTP enters the picture in 1989. While at CERN, Tim Berners-Lee proposed a new system for helping keep track of the information created by "the accelerators" (referencing the yet-to-be-built Large Hadron Collider) and experiments at the institution. He embraces two concepts from Nelson:

1. Hypertext, or "Human-readable information linked together in an unconstrained way,"
2. and Hypermedia, a term to "indicate that one is not bound to text."

In the proposal he discussed the creation of a server and browsers on many machines that could provide a universal system.