Air actuators are devices that create mechanical motion by converting various forms of energy (in the case of this website - compressed air) into rotating or linear mechanical motion.
The air actuator converts the energy stored in compressed air into mechanical energy. The compressed air is then able to create motion or to do work, by attaching devices to the actuator rod or shaft.
An image of a typical air actuator follows, this one manufactured by Norgren.
If you are looking for them, here is a a selection of air actuators for your review.
There are a wide variety of linear and rotary actuators commercially available. Options for them include electric or hydraulic actuators, or the actuators we are primarily concerned with on this site, compressed air actuators.
Having a bit more information about types of actuators will help in determining which will be best suited to your application.
If yours is a high cycle, high speed application, electric actuators wouldn't be your first choice. They don't normally provide the speed that an actuator driven by compressed air can.
For precise positioning of tooling, the first choice is often the electric actuator. They can provide positioning to tighter tolerances than most air cylinders can. Also, where compressed air is not readily available, an electric actuator can be the option of choice.
Here are some options if you need an electric actuator.
With hydraulics you can generate much more force from a much smaller actuator than is possible with air.
This power to size superiority comes at a higher cost over comparably sized pneumatic components. If it's high brute force required with thousands of pounds of force being needed, or you need to generate relatively high force in a very small footprint hydraulic actuators are called for. Or, perhaps where there isn't room for a pneumatic actuator of the size necessary to provide the force the application requires and you need to generate force in a smaller package. That's where hydraulic actuators, albeit with their higher cost, shine!
Generally speaking, if you can generate the force you need with compressed air, and the actuator footprint isn't an issue, and your application doesn't require precise positioning of the actuator rod soleley by compressed air, then air cylinder actuators would be your first choice. They are easy to obtain, have simple operation and are relatively low cost.