HTTP is a transfer protocol used by the World Wide Web (WWW) to retrieve information from distributed servers. The HTTP model is extremely simple; the client establishes a connection to the remote server, then issues a request. The server then processes the request, returns a response, and closes the connection. Most HTTP communication is initiated by a user agent and consists of a request to be applied to a resource on some origin server. HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80, but other ports can be used like 21 (FTP), 443 (HTTPS).