detects an incoming signal and respond by changing something in the environment. For example, a relay is an actuator that toggles a mechanical switch, and can thus cause a good number of responses to occur such as enabling illumination, heating system, audible alarm, and so on. Actuators such as motors, pneumatics, and hydraulics can move objects and pump fluids.
[is] a mechanical device for moving or controlling a mechanism or system. It takes energy, usually transported by air, electric current, or liquid, and converts that into some kind of motion.