A WikiWikiWeb is a collaborative hypertext document produced by a community of users by means of a WikiWiki tool.
The original WikiWikiWeb was established by Ward Cunningham, who invented and named the Wiki concept, and produced the first implementation of a WikiWiki server. Many Wikis are immediately identifiable by their use of CamelCase, mixed case words that turn into automatic links.
Ward's Wiki remains one of the most popular Wiki sites:
You can search the page titles of various wikis at once using MetaWiki.
The particular Wiki you are looking at is Wikipedia, an effort to write a complete encyclopedia from scratch, collaboratively. It is currently adding articles at a pace of a thousand or so per month.
See also: What is a wiki, History of wiki