I have noticed that when I write a post there is a "Community Wiki" check box I can select. I have also noticed that sometimes questions will be converted to community wiki if they are deemed "off topic" (according to the rules of the FAQ).
How exactly does a community wiki question work and how should it be used? Also, why are some "off topic" questions converted to community wiki?
I could add that the description of the "Cast close and reopen votes" privilege don't mention community wiki.