<p>There is a definition of "Community Wiki" available on the <a href="http://meta.stackexchange.com/questions/11740/what-are-community-wiki-posts">Stack Overflow meta site</a>. As far as I know the information there applies to all other sites built on the Stack Exchange engine.</p>

<p>As I understand it a community wiki question is owned by the whole community instead of an individual user. As a result a lower bar is set for the reputation score needed to do certain things (like edits), and up/down votes do not have the affect reputation scores they would on a normal question.</p>

<p><strong>Update:</strong> As <a href="http://meta.ubuntu.stackexchange.com/questions/154/where-are-the-community-wikis/167#167">noted here by Erigami</a> and <a href="http://meta.ubuntu.stackexchange.com/questions/160/finding-community-wikis/166#166">this answer</a> on the Finding community wikis question, a list of community wiki questions can be obtained by using the search term "wiki:1". Here's a link to the results of that search on the parent site:</p>

<p><a href="http://ubuntu.stackexchange.com/search?q=wiki:1">http://ubuntu.stackexchange.com/search?q=wiki:1</a></p>

<p><strike>I am not aware of any method to get a definitive list of questions that have been set to community wiki.</strike></p>