An actuator is the mechanism by which an agent acts upon an environment. The agent can be either an artificial intelligence agent or any other autonomous being (human, other animal, etc)

a mechanism that puts something into automatic action is called an actuator.

Some examples of actuators of these various agents include:

• Human - Arms, hands, fingers, legs
• Part picking robot - Grasping mechanism, moving parts. Examples include solenoids and voice coil actuators.
• Mail transfer agent - Update software

In engineering, actuators are a subdivision of transducers. They are devices which transform an input signal (mainly an electrical signal) into motion. Electrical motors, hydraulic pistons, relays, comb drive , piezoelectric actuators, thermal bimorphs, Digital Micromirror Devices and electroactive polymers are some examples of such actuators.

Motors are mostely used when circular motions are needed, but can also be used for linear applications by transforming circular to linear motion with a bolt and screw transducer. On the other hand, some actuators are intrinsically linear, such as the piezoelectric actuators for example.

See also switch, telepresence, touch, muscle.