What is a Wiki?

noun: wiki; 
a website that allows collaborative editing of its content and structure by its users.

It’s like a hotel visitor book. As opposed to a hotel brochure. The content is made up entirely of public contributions. Are you ready to contribute? See the list of Category:Articles needing attention or create a new article.

It’s like the wiki wiki bus. Howard Cunningham, the developer of WikiWikiWeb in 1995, learned the word on a visit to Hawaii Airport, where he was told to take the wiki wiki bus between the airport terminals. It means ‘superfast’ –- appropriate as the open nature of Wiki sites means they can grow exponentially.

(from the Sideways Dictionary web site)