WWW or World Wide Web typically refers to web servers throughout the world which are all accessible typically with a normal computers web browser software such as Internet Explorer, Safari and Firefox to name a few. The various web servers are all linked via hypertext documents which are interpreted by the browsers according to accepted standards and may contain text, images, videos and other pieces of compatible content.
The concept of the World Wide Web was originally for a limited implementation at a specific research facility to help allow information to be available to anyone who wanted to look at it. But there was a realization that it could be implemented all across the world for all kinds of information and so the idea was proposed on a newsgroup in 1991. At that time the entire WWW consisted of a single Next computer acting as the server and a freshly written browser called WorldWideWeb (all one word) which could read and also edit pages.
The three primary components that make the World Wide Web possible are Universal Resource Locators (URL), Hypertext Markup Language (HTML) and Hypertext Transfer Protocol (HTTP). With these three components, web pages may be placed online, written in such a way as to be interpreted by web browsers conforming to HTML standards, and transferred from one computer to another through HTTP. While many additions to types of content and ways to write web pages have been invented since then, the basics are still essentially the same.