A distributed information service that was developed at CERN, the European Laboratory for Particle Physics, Geneva, in the early 1990s. The Web is a large-scale distributed hypermedia system that is based on cooperating servers attached to a network, usually the Internet, and allows access to ‘documents’ containing ‘links’. It is accessed using a workstation that is connected to the network and is running a suitable utility program, usually a web browser.

Within the Web, documents are presented in hypertext mark-up language (HTML), and may consist of textual material or a number of other forms, such as graphics, still or moving video images, or audio clips. Within a document there will be material to be displayed and usually one or more links, which in a text document appear as highlighted words or phrases, or as icons. The links hold embedded pointers to other documents located elsewhere on the Web by the use of a URL. A URL contains information specifying the network protocols to be used, the network address of the server holding the document, and the local index entry for that document. Activating a link, typically by positioning the mouse pointer over the highlighted text and clicking, will cause the workstation to connect via the network to the corresponding server, load the document and the means of presenting the document, and display the document. Browsers also allow the workstation to download programs and other files, either for immediate execution or to be saved for future use. Such files are a major source of malware.