An outrunner motor is the most common type of brushless motor found in RC planes. In this design, the outer shell (or rotor) rotates around a fixed internal stator.
Outrunners typically have higher torque, which means they can turn larger propellers at lower speeds without needing a gearbox. Since the outer case rotates, it helps with air circulation, which can improve cooling. This allows the motor to run cooler for longer periods. Also, due to their higher torque, outrunner motors are generally direct-drive—no need for gearboxes to step down the speed, making them easier to install.
Outrunners usually have a lower Kv (RPM per volt) rating, meaning they are better suited for slow and stable planes, like trainers, gliders, and larger scale models.