What are wikis and what are they for?

"A Wiki can be thought of as a combination of a Web site and a Word document. At its simplest, it can be read just like any other web site, with no access privileges necessary, but its real power lies in the fact that groups can collaboratively work on the content of the site using nothing but a standard web browser. Beyond this ease of editing, the second powerful element of a wiki is its ability to keep track of the history of a document as it is revised. Since users come to one place to edit, the need to keep track of Word files and compile edits is eliminated. Each time a person makes changes to a wiki page, that revision of the content becomes the current version, and an older version is stored. Versions of the document can be compared side-by-side, and edits can be "rolled back" if necessary.

"The Wiki is gaining traction in education, as an ideal tool for the increasing amount of collaborative work done by both students and teachers. Students might use a wiki to collaborate on a group report, compile data or share the results of their research, while faculty might use the wiki to collaboratively author the structure and curriculum of a course, and the wiki can then serve as part of each person's course web site." -- from "Using Wiki in Education" by Stewart Mader

This Common Craft video explains it all