A shaded pole motor is a single phase induction motor. The "pole shading" is a shorted turn of wire a wrapped around part of the motor poles. This creates a phase shifted magnetic field which is a starting field for the motor (this is used instead of a start winding). Impedance protected means that the motor shaft can be stalled without overheating the motor; thus a fuse or thermal cutout is not needed.
This type of motor is made in fractional HP sizes only because of low efficiensy. They are most often used for small fan motors.