Wiki-Wiki what

What's a wiki? My husband thought it was a young wookie, but he's weird. A wiki is a user generated site where anyone can edit and post anything, anytime. Sounds like a disaster waiting to happen, right? But it's not. Because when people post on the most popular site, Wikipedia.org, there are thousands of other people who are just as passionate about the subject as the people who might vandalize or put false information on the page. Wikipedia makes the user the editor, so there are more guardians of the gateway of information, making points of failure harder to slip through the cracks. How could you use a wiki in your classroom, and is it appropriate for younger students such as second graders?