The World Wide Web ("the Web" or "WWW" for short) is a hypertext system that operates over the Internet. To view the information, one uses a piece of software called a web browser to retrieve pieces of information (called "documents" or "web pages") from web servers (or "sites") and display them on the user's screen. The user can then follow hyperlinks on the page to other documents or even send information back to the server to interact with it. The act of following hyperlinks is often called "surfing" the web.
Just as one can distinguish between "an internet" and "the Internet", one can refer to "a web" as a collection of sites providing information by the means described here (perhaps on an intranet), and "the Web", which is the single, large, interconnected web available on nearly all public Internet sites.
The Web grew out of a project at CERN, beginning around 1989, where Tim Berners-Lee built the prototype system that became the core of what is now the World Wide Web. The original intent of the system was to make it easier to share research papers among colleagues. The original name of the first prototype was Enquire Within Upon Everything.
The core functionality of the Web is based on three standards: The URL, which specifies how each page of information is given a unique "address" at which it can be found; HTTP, which specifies how the browser and server send the information to each other, and HTML, a method of encoding the information so it can be displayed on a variety of devices. Berners-Lee now heads the World Wide Web Consortium, which develops and maintains these standards and others that enable computers on the the Web to effectively store and communicate all kinds of information.
The initial "www" program at CERN only displayed text, but later browsers such as Pei Wei's Viola (1992) added the ability to display graphics as well. Marc Andreesen of NCSA released a browser called "Mosaic for X" in 1993 that sparked a tremendous rise in the popularity of the Web among novice users. Andreesen went on to found Mosaic Communications Corporation (now Netscape Communications). Additional features such as dynamic content, music and animation can be found in modern browsers. Frequently, the technical capability of browsers and servers advances much faster than the standards bodies can keep up, so it is not uncommon for these newer features to not work properly on all computers.
Another significant advance in the technology was Sun Microsystems Java programming language, which enabled web servers to embed small programs (called applets) directly into the information being served that would run on the user's computer, allowing faster and richer user interaction.