Contrary to what many people think, the Web is not the Internet, but is a network within the Internet.
The World Wide Web, also called WWW or W3 is a hypertext based information system, that is the largest single segment of the Internet.
Hypertext is a way of linking related items of information without regard to their physical location. Any word in a hypertext document can be specified as a pointer to, or a link to, a different hypertext document where more information pertinent to that word can be found. Using different selection methods depending on the interface, the reader can open the second document by selecting the linked word in the first document; only the part of the linked document which contains relevant information will be displayed. In a mouse based system, a user would place the mouse over the word or link and click the mouse button
The second document may itself contain links to further documents. Readers need not know where the referenced documents are, because they will be obtained and presented as they are needed. The World Wide Web uses hypertext over the Internet; the linked documents may be located anywhere on the planet, to the user it does not matter. All of these links create a web which spans the globe, hence, the World Wide Web.
Users access the World-Wide Web facilities via a client software called a browser, which provides transparent access to the WWW servers. The browser also provides access to many other tools on the Net so has become the major means of access to Internet resources.
The term document is used rather loosely. A hypertext document can more than link to words; it can display pictures, play sound and video, or transfer software.