8 Pole Heli Motor in an E Revo?

Ok,this is a really stupid question,but I have never seen or used one before so I guess it's a legitimate question? What makes an outrunner an outrunner? And what benefits do they provide over a typical Bl setup,and why are the kv's so low when compared to a regular Bl on the same battery? Aside from my questions,that is a good looking setup Sikeston!--Josh