These answers are not set in stone. Just my experience from running a fourm.
Admin: This level can access the forum software, and is the highest level of management on a forum.
Super Mod: I believe this level can moderate any forum. Might also have some special functions.
Mod: Moderates just the forums assigned. Can not make changes to other forums.
Does that help? Just think of it as different levels of management. The higher you go, the more functions/capabilities/responsibilities the individual has.