Wiki is a web application with which users can edit entries at will. The best known wiki around is the
Wikipedia, a pretty comprehensive encyclopedia run on the wiki system.
The plus is that it's a constantly growing database, with anyone who knows what they're talking about being able to give input. Things can easily be corrected and updated with little work on the part of the adminsitrator.
The bad news is, it's open to incorrect info. Fortunately, you can as an administrator elect to review any input before it gets merged into the live article. Plus, wiki automatically saves previous versions, so if someone erroneously changes something (or screws up formatting), it's easy to revert.