A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator.

Mechanical efficiency is the ratio of actual torque delivered to theoretical torque. Torque ripple is the difference between minimum and maximum torque delivered at a given pressure during one revolution of the motor. Motor speed is a function of motor displacement and the volume of fluid delivered to the motor.