from wikipedia: A wiki is a page or collection of Web pages designed to enable anyone who accesses it to contribute or modify content, using a simplified markup language. Wikis are often used to create collaborative websites and to power community websites. The collaborative encyclopedia Wikipedia is one of the best-known wikis.
Wikis are useful tools for collaboration (with other members of your team, with artists interested in the same issues/media, or with the general public) and become an excellent repository of information for anyone else – the public or new members to your team.
Wikis are relatively easy to set up and build. The text based interface and collaborative nature allow for many users to work on the project simultaneously.