Controller (control theory)

Controller is like a machine or person that helps make sure something goes according to plan. In control theory, a controller is a device or program that looks at the current state of something, like a system or a machine, and then tells it what it should do next in order to keep it on the right track. For example, the controller could tell a machine to turn left if it is drifting to the right, or it could adjust the temperature of an air conditioner if the room was getting too hot. Controllers are used in many different types of systems, from planes and cars to robots and computers.