Proportional control is a method used in control systems to maintain a desired output by adjusting the input based on the difference between the desired setpoint and the current value. This difference is known as the error. The control system applies a correction that is proportional to this error, meaning that larger errors result in larger corrections. This technique is commonly used in various applications, such as thermostats for temperature control and motor speed controllers. By continuously adjusting the input based on the error, proportional control helps systems respond effectively to changes and maintain stability.