From e107 Wiki
A Wiki or wiki (pronounced "wicky" or "weekee") is a website (or other hypertext document collection) that allows any user to add content, as on an Internet forum, but also allows that content to be edited by any other user.
The term can also refer to the collaborative software used to create such a website.
Wiki (with a capital 'W') and WikiWikiWeb are sometimes used to refer to the Portland Pattern Repository, the first ever wiki. Proponents of this usage suggest using a lower-case 'w' to distinguish the generic terms discussed here. Wiki wiki comes from the Hawaiian term for "quick" or "super-fast".
Sometimes wikiwiki or WikiWiki are used instead of wiki. The terms are interchangeable though the aforementioned differing views about capitalization also apply analogously.
A wiki enables documents to be written 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".
A defining characteristic of wiki technology is the ease with which pages can be created and updated. Generally, there is no review before modifications are accepted, and most wikis are open to the general public — or at least anyone who has access to the wiki server. In fact, even registration of a user account is not always required.