Commoncraft does another great job at explaining what a wiki is. Watch their video directly from the Wetpaint Wiki site. Click on the video on the left side of your screen.

This is a Wetpaint Wiki. A wiki is a website set up for you to create, add to, collaborate in, change, edit, thoughts and content.

The worlds biggest Wiki that I can think of is Wikipedia. It is sometimes frowned upon for students to use wikipedia as a source for their research, but I say it should be considered as one of their sources. It may not be the main source, but it can be a starting point or an informational site . Wikipedia is the largest encyclopedia online and can be updated and edited by anyone. Read About Wikipedia and the amazing statistics. It is argued that it is one of the most instantaneous, direct lines of communication and transferrence of current events available to us in the world. It can report news faster than the television or radio. It is instantly updated with live footage, photos, and editorials of what is happening at that very moment. Where else on this planet can people share such amazing and immediate knowledge?

Why would I use a wiki in education?
I was fortunate to judge a global learning project called Horizon Project 2008 this year that was created on a wiki. This global learning project was inspired by the book, The World Is Flat by Thomas Friedman. The project started as The Flat Classroom project and evolved over time into the new Horizon Project. The educators, Vicki Davis (Camilla, Georgia) and Julie Lindsay (Qatar Academy), have won numerous awards in the technology field through their wonderful collaborative work. The wiki enabled the students from all over the globe to collaborate on a project in one learning environment. There was no need for email and piecing parts of the project together. With equal access to the same page, every member of each team is able to edit their page and add content.