(HyperText Transfer Protocol) The communications protocol used to connect to Web servers on the Internet or on a local network (intranet). Its primary function is to establish a connection with the server and send HTML pages back to the user's browser. It is also used to download files from the server either to the browser or to any other requesting application that uses HTTP.

Addresses of Web sites begin with an http:// prefix; however, Web browsers typically default to the HTTP protocol. For example, typing www.yahoo.com is the same as typing http://www.yahoo.com. In fact, only yahoo.com has to be typed in. The browser adds the rest.

HTTP vs. HTTPS
With HTTP, the Web page is transmitted without any encryption. However, HTTPS (HTTP Secure) is used to encrypt sensitive data such as credit card and social security numbers (see HTTPS).

A Stateless Connection
HTTP is a "stateless" request/response system. The connection is maintained between client and server only for the immediate request, and the connection is closed. After the HTTP client establishes a TCP connection with the server and sends it a request command, the server sends back its response and closes the connection.

The first version of HTTP caused considerable overhead. Each time a graphics file on the page was requested, a new protocol connection had to be established between the browser and the server. In HTTP Version 1.1, multiple files could be downloaded with the same connection. It also improved caching and made it easier to create virtual hosts (multiple Web sites on the same server). See HTTP header and cookie.