Wiki is a piece of server software that allows users to freely create and edit Web page content using any Web browser. Wiki supports hyperlinks and has a simple text syntax for creating new pages and crosslinks between internal pages on the fly.
Wiki is unusual among group communication mechanisms in that it allows the organization of contributions to be edited in addition to the content itself.
The most famous of the Wikis is Wikipdia, which has become as common as google for finding information. In fact, lots of Google search bring up a Wikipedia entry.
And now...The Exchange 2007 Beta Wiki, better than a newsgroup, the perfect place to ask a question or donate information on this new and exciting product.
Right now there is not a whole lot of information, but this will probably fill up by the next release.