A Wiki is a free, online writing space that is ideal for collaboration. While a web page can be read, a wiki can be read and edited by other users. A wiki is created by a group of individuals. With password access individuals can submit information or edit information on the wiki. The wiki’s history shows all the changes that have been made, so contributors and visitors can see the changes over time.

A great wiki on wikis. View the screencast on how wikis work - created by Dean Shareski, Moose Jaw

How can teachers use wikis to facilitate teaching and learning?

• Provide a space for online writing and collaboration beyond the classroom walls
• Student Journaling – to demonstrate the writing process, to expose understanding (and misunderstanding) and to reflect upon learning
• Personal Scrapbook – A space to create a collection of notes, images, or web links for a topic of study
• Collaborative Knowledge Building Space -  Promote collaborative group writing on a topic. May be project development space, or a piece of a larger class project.

Resources for creating a wiki
WikiSpaces
Wikispaces is an outstanding tool that's free for K-12 educators, and more important, it's free of advertising.