An actuator refers to a device used to control or move a system or mechanism. A camshaft actuator is used to control camshaft timing.
A camshaft is a shaft attached to the cam. This is the rotating piece in a mechanical linkage designed to convert circular motion into straight-line motion. The actuator is used to provide thrust to the base of the camshaft shaft.
Timing between the rotation of the crankshaft and camshaft is integral to the proper function of a vehicle engine. The crankshaft refers to an engine part used to convert reciprocating linear piston motion into rotational motion. The camshaft operates the poppet valves, which control both exhaust gases and the air-to-fuel mixture flow. The valves must close and open at the necessary points during the piston stroke to transfer the gases and mixture. This timing is facilitated via the actuator.
The camshaft actuator mounts to the end of the camshaft and either slows or speeds up the opening and closing of the poppet valves via commands sent by the Engine Control Unit. This enables valve timing to be more precise, which helps optimises engine performance.