When a question reaches 5 close votes, it is marked as closed, and will no longer accept answers. Closed questions may be opened by casting reopen votes in the same manner. However, you may only vote to close or reopen a question once.
So I would figure that it takes five users to close a question like this one, but it only lists two.
Now this one took five before it was closed.
What is the difference between these two questions and why does a question close after less than five votes sometimes?