A wiki is a collaborative website that allows multiple contributors and/or visitors to add, delete and edit content on a particular webpage quickly and easily.  Generally, no coding or HTML knowledge is necessary. Named after the wiki wiki bus in Honolulu, the term means quick in Hawaiian.  Features include  an edit tab, a discussion tab, and history of changes tab.  Businesses and organizations employ wikis to disseminate information and work collaboratively. In academic settings,  departments and committees use the technology to develop reports,  write policy statements and author curriculum material.  Students work on team projects, create lab reports and develop research assignments.

There are two basic ways to get started with a wiki. You can use a web-based wiki farm that hosts your wiki on its server, or you can download wiki software to your own server.  The first is simple but does not have a great deal of flexibility, while the second offers more customization but requires a higher level of expertise.  Check out  the examples below, some of which are  free, some fee-based, and some  free but with a premium version.

Web Hosted Wiki Farms

http://pbwiki.com
http://wikia.com
http://www.wetpaint.com
http://www.seedwiki.com

Wiki Software 
http://twiki.org
http://tikiwiki.org
http://www.pmwiki.org