Power Bottom?

My buddy was telling me about his gay friend who claims to be a "power bottom." I'm familiar with the term, but what does it mean? Does it mean you don't cry when you take it in the ass? That reflects a good deal of power, I would say. Does it mean that you aggressively back up onto the dick instead of just taking it? Because that kind of aggressiveness would be an indication of power, too, I suppose. I'm confused. Someone enlighten me.