HTTP means HyperText Transfer Protocol. HTTP is the underlying protocol used by the World Wide Web. HTTP is a protocol that defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.
HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it. This is the main reason that it is difficult to implement Web sites that react intelligently to user input. This shortcoming of HTTP is being addressed in a number of new technologies, including