Definition: "A wiki is a website that can be edited over a web interface. Sounds like just another weblog? Not really. Wikis are typically open to all comers interested in the topic at hand, making them excellent resource-building tools. Also, their pages form more of a semi-permanent network of organised information than the ephemeral time-based entries of blogs."
One way it's used: "Tyson Clugg, a wiki enthusiast and president of the Melbourne Wireless Group, says his group uses its wiki to write technical documents because it allows several people to work on the same document without having to know who has the "live copy". "
Where the name originated: "Ward Cunningham, of the site c2.com, based in Portland, Oregon, invented not only the wiki, but the name wiki-wiki, as slang for "quick web", based on the Hawaiian word for quick."
Try it out yourself: "And like blogging, there are "wiki farms" where non-commercial users can build wikis for free - seedwiki.com is just one."