What is a wiki?

From Free Definition:

A WikiWikiWeb enables documents to be authored collectively in a simple markup language using a web browser. Because most wikis are web-based, the term "wiki" is usually sufficient. A single page in a wiki is referred to as a "wiki page", while the entire body of pages, which are usually highly interconnected, is called "the wiki".

"Wiki wiki" means "fast" in the Hawaiian language, and it is the speed of creating and updating pages that is one of the defining aspects of wiki technology. Generally, there is no prior review before modifications are accepted, and most wikis are open to the general public or at least to all persons who also have access to the wiki server. In fact, even registration of a user account is not often required.

Now you know.