"A wiki is a medium which can be edited by anyone with access to it, and provides an easy method for linking from one page to another. Wikis are typically collaborative websites, though there are now also single-user offline implementations. Ward Cunningham, developer of the first wiki, WikiWikiWeb, originally described it as "the simplest online database that could possibly work".^[1] One of the best-known wikis is Wikipedia.^[2]"

"Wiki." Wikipedia. WikiMedia Foundation. 7 Oct 2007 http://en.wikipedia.org/wiki/Wiki

Video from Commoncraft--Wikis in Plain English

Resources

The Art and Technique of Wikis--A wiki created by David Warlick.  This wiki was created to share information and workshop notes on the educational use of wikis.  This is a rich resource for those new to wikis.

How I Use Wikis--A very informative blog article courtesy of Vicki A. Davis at Cool Cat Teacher Blog on how she uses wikis in the classroom. 

Wikispaces--A website that provides free public wikis to anyone.  Public wikis do contain advertisements.

PBWiki--A website that offers free wikis that can be made public or private and are advertisement free.

Yugma--A website that provides free web conferencing and desktop sharing online.

Google Docs--Google's free service that allows users to create, upload, publish, and share word processing documents, spreadsheets, and multimedia presentations.  A live chat feature is also available so you can chat real time with fellow collaborators as you edit the document together.