(WWW, W3, the web) A client-server hypertext distributed information retrieval system, often referred to as "The Internet" though strictly speaking, the Internet is the network and the web is just one use of the network (others being e-mail, DNS, SSH).
Basically, the web consists of documents or web pages in HTML format (a kind of hypertext), each of which has a unique URL or "web address". Links in a page are URLs of other pages which may be part of the same website or a page on another site on a different web server anywhere on the Internet.
The URL "scheme" (the bit before the ":") indicates the protocol to use. These include FTP, the original protocol for transferring files over the Internet. RTSP is a streaming protocol that allow a continuous feed of audio or video from the server to the browser. Gopher was a predecessor of HTTP and Telnet starts an interactive command-line session with a remote server.
The web is accessed using a client program known as a web browser that runs on the user's computer. The browser fetches and displays pages and allows the user to follow links by clicking on them (or similar action) and to input queries to the server. A variety of browsers are freely available, e.g. Google Chrome, Microsoft Internet Explorer, Apple Safari and Mozilla Firefox. Early browsers included NCSA Mosaic and Netscape Navigator.
Queries can be entered into "forms" which allow the user to enter arbitrary text and select options from customisable menus and other controls. The server processes each request - either a simple URL or data from a form - and returns a response, typically a page of HTML.
The World-Wide Web originated from the CERN High-Energy Physics laboratories in Geneva, Switzerland. In the early 1990s, the developers at CERN spread word of the Web's capabilities to scientific and academic audiences worldwide. By September 1993, the share of Web traffic traversing the NSFNET Internet backbone reached 75 gigabytes per month or one percent. By July 1994 it was one terabyte per month.
Following the widespread availability of web browsers and servers from about 1995, organisations started using the same software and protocols on their own private internal TCP/IP networks giving rise to the term "intranet".