Ais a web site made up of content posted by users. each page has an "edit" link.

A wiki page is made up of collaborative content by users who can edit and delete content as it is seen fit.  These pages began out on Wikipedia, as the name can tell, but they have spewed into other genres of internet content.  A lot of wiki pages have been made for certain subcultures and groups, and these guys have the same general idea.  Anyone can edit and do whatever with it, and that's why you can't use it as a reliable source in school.