As for outrunner motors like MTM, the reason for this term is that the magnets rotate around the outside of the stationary windings, versus the magnets rotating inside of the windings as in the earlier breeds. In the out-runner motors, the rotating outer case conveys the rotary motion to the prop shaft.
The advantage an out-runner style motor has over the conventional brushless motor like Hacker makes, is a marked improvement in torque. With the magnetic force being applied at a greater distance away from the pivot point, a greater torque is obtained for the same electrical power consumption.
But, the increase in torque is offset by a loss in RPM capability. The centrifugal forces involved would tear the outer case apart if run at the same speeds as a conventional brushless.
How coincidental it is, then, that we always take high-speed motors, gear them down, and sacrifice the high speed for torque anyway? Seems like theres a step in there that we could avoid altogether, and thats exactly why the three MTM motors center around eliminating the need for a gearbox.
I hope this article sheds some light on the subject of motors, especially Hacker Brushless and the affordable MTM outrunners pictured above.