HTTP is an Acronym for Hyper Text Transport Protocol.
A simple protocol that constitutes the foundation of the WorldWideWeb, sometimes called "How To Transfer Porn". The default Port for HTTP is 80. A lot of people love doing all sorts of unnecessary things over HTTP such as use for RPC implementations (which are then called Web services).
We're currently up to version 1.1 of the protocol; see 
RFC:2616. You may be interested in 
the original proposal that started it all, or in the protocol's error codes.
37 pages link to HTTP:
lib/main.php:944: Notice: PageInfo: Cannot find action page