Ding ding ding!
I actually hinted at this in the
example page:
You are given the choice to enter a name for the forum to be accessed by (the "slug", if you're familiar with WP). The advantage is that you don't have an ID. The disadvantage is that you basically can't change this without breaking existing links to it.
It's specified on a per forum basis, and yes it has to be unique. The ID based version will still work.