<p>These questions on Meta Stack Overflow seem relevant:</p>

<ul>
<li><a href="http://meta.stackexchange.com/questions/11740">What are “Community Wiki” posts?</a></li>
<li><a href="http://meta.stackexchange.com/questions/55888/when-to-mark-the-community-wiki-checkbox-on-a-new-question">When to mark the ‘community wiki’ checkbox on a new question?</a></li>
</ul>