Collaborative Document Production
Wiki web pages are part of the Web 2.0, where they can be used for collaboration. Any person viewing a wiki page can be a contributor/editor without needing direct access to a server. These contributions can include: changing the outline of the page, editing content and adding additional content or pages. Ideally, anyone who reads a page could edit, however there are multiple levels of access that can be set. Because of the ease of contributing, there is metadata (Who, What, When) attached to the page. The "History" tab at the top of each page shows the time-sequence of edits and allows reverting back to any of its previous versions. Thus, content is never deleted, just shoved to the background.
The wiki is self-regulating because spam and other bad information is quickly removed by the community and good stuff tends to be preserved.