I'm trying to make wings that fold in and open. I want to have the joint of the wing controlled by a motor of some sort but I don't know what I'm looking for is called.
The general term is a rotary actuator, which includes servomotors and hydraulic / pneumatic actuators.
But, being a wing, probably you do not have space for an actuator directly on the elbow, and need a cable + pulley setup with a linear actuator elsewhere. It depends a lot on your space constraints.