The copyright note at the bottom of the site says that all content is available under the Creative Commons Attribution-ShareAlike 2.5 license.
This basically means that people can use, share, adapt, and retransmit content you generate for pretty much any purpose, so long as they attribute the original to you and also share it/their adaptation under a similar license.
It's pretty impossible to restrict the content any further than that. Wikis work on the fact that once you post something, everyone else is free to adapt it. The wiki couldn't operate if they had to keep track of which contributions are restricted in different ways (even the way Wikipedia does with images is fairly complicated if an adaptation were made).