Public groups?

Probably a stupid question:

What are public groups?

In all profiles they say "x" is not a member of any public groups...

Like, reviewers, moderaters, admins. I think. If you're not part of any, you're just... member.

Actually, those aren't public groups. I'm pretty sure we haven't implemented public groups at all.

Yeah, there aren't any public groups (which, in case anyone is wondering, are alternate groups joinable at any member's discretion), because as far as I can tell, we don't yet really have any use for them.