A can shaped direct current motor.
The stator is built using permanent magnets, the rotor has windings which are energized during operation. Polarity is controlled using a commutator and brushes.
Most Direct Current motors used for models are permanent magnet motors.
When operated using zero stretching, the motor will hum. The motor may also hum when the decoder supplies pulses for low speed operation, adjusting the CV that controls the pulse frequency may minimize or eliminate it.
Some are 5 Pole Skewed motors. The rotor has five poles, which are skewed, for better low speed operation without cogging.