A wiki is an interactive web document that users can edit collaboratively. Instead of making changes to individual documents, and having someone rectify differences between multiple documents, all users of a wiki can make changes in the same document. All users are able to see the same version of the document, and students can compare previous versions of the wiki.
About Wikis
Please click this link to view a video that provides a more detailed explanation about how a wiki works.
Students can edit notification settings for Wikis in the Activity Stream.