What is a Wiki?
Wiki is web server software that allows users to contribute content. Collaboration is the key to Wiki, which is designed as a powerful system for online communities to build web pages and web sites. Unlike blogs and forums, all users are allowed to contribute and edit existing content. Wiki is derived from the Hawaiian term "wiki wiki" meaning "quick". The concept behind a Wiki is that collaboration on projects will move it along quicker.
Wikipedia - Wikipedia is a popular content encyclopedia that anyone can edit. http://www.wikipedia.com