Hydraulic actuators convert fluid pressure into mechanical motion or force. There are three main types: linear actuators like cylinders provide straight-line motion, rotary actuators like motors provide rotational motion, and semi-rotary actuators provide limited angular motion. Hydraulic cylinders are the most common linear actuator. Cylinder types include single-acting, double-acting, telescopic, and tandem cylinders. Cushioning devices are used to control cylinder deceleration and prevent shocks at the end of the piston stroke.