Wikis are variations of the conventioal Web Sites that allows collaborative maintenance of content (additions, deletions, and updates) by known or anonymous authors. They provide an agile platform for "rapid fire' content production and dissemination.
Wiki content editing is typically performed via a browser using the Wiki Engine specific Markup Language. These engine specific Markup Languages are shorthand style languages that are post processed by a Wiki Engine into (X)HTML when Wiki documents are retrieved by HTTP based User Agents (e.g Web Browsers).
Wikis are knowledge creation, persistence, dissemination tools. They facilitate the construction and standardization of vocabulary across a collection of articles (typically called a Web or Cluster). In a sense, they create a body of broadly accessible knowledge.
Wikis can be categorized as knowledge engineering tools that provide a productive platform for knowledge creation and dissemination to knowledge workers.
-- KingsleyIdehen - 28 Mar 2006