A Wiki is website that can be created and edited very easily. One of it's features is that it allows for collaboration from many different people in creating or contributing to the Wiki. A Wiki can have many uses in the education world. One beneficial way to use a Wiki is to provide resources for parents and students to use at home that support the instruction that is going on at school. Currently, our school has a Math Wiki that was created by one of our teachers a few years ago. The address is http://mathfocus.hcpss.wikispaces.net/. The purpose of this particular Wiki is to provide math resources for parents and students to use in one easy to access place.
Another educational use for a Wiki could be to have the students edit a Wiki that was created by their teacher. The teacher could create a Wiki with a set of directions telling the students what their assignment is. The students would then have to add things to the Wiki in accordance to what the assignment is. The students might have to respond to a question, create a story, edit something the teacher has written, or create a project of some kind. You could even have the kids work in groups to edit and work on their assignments. One nice thing is that the students can put their work right on the Wiki due to it's collaborative nature.
If you are interested in creating a Wiki of your own, here is a great website resource that will walk you through it: http://www.wikispaces.com/. You can even create a free classroom Wiki with some great features!