A wiki is a collaborative space where many people may work together to share knowledge. The most well known example of this is Wikipedia, where people from around the world work together to share and pool information to create an encyclopedia of terms, much larger than would be possible by an individual. However, not all wikis have to be used as encyclopedia of terms, they can be used privately by a group of people to develop a collaborative document, This could be anything from a project plan, article or camping list. A useful feature is their ability to be easily searched and linked to other related knowledge. Another example of how a wiki can be used is this space right here! The UCL wiki offers everyone there own space and is used by many teams (such as E-Learning Environments) to create an collaborate on documentation, guides and knowledge based articles.
Wikis allow people to collaborate on text based documents, share media and documents and comment on each other's work. Once saved a new version is created, so you can always retrieve work if it is modified or deleted. You can also use the revision history to see who has contributed what.
Most sites are FREE and community driven.