A motor, not necessarily electric, which converts energy into some kind of motion.
A motor, not necessarily electric, which converts energy into some kind of motion. More generic than motor which is usually assumed to be both electric and rotary.
From the Wikipedia page:
An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. 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.).