I'm seeing posts show up that are labeled "community wiki." What are these? It's not a tag and I can't list them all. Can anyone explain?
You make a wiki by checking the box at bottom right, when editing a Q/A. This does several things.
It makes the question owned by the Community, so anyone (above a certain rep) can edit them.
You neither gain nor lose reputation based on votes.
It's intended for Questions that are not really good single-Answer type questions - if they are subjective, or have no single right answer ("what's a good gamedev book"), so you couldn't checkmark one as best.
Update - you can no longer make a Question into a wiki (unless you're a moderator).
These questions on Meta Stack Overflow seem relevant: