A rheostat is an electrical device used to control the flow of current in a circuit by varying resistance. It consists of a resistive wire or element and a sliding contact that moves along the wire, allowing users to adjust the resistance and, consequently, the current. Rheostats are commonly used in applications like dimming lights or controlling the speed of motors. These devices are often found in lighting systems, electric fans, and industrial equipment. By changing the resistance, a rheostat can help manage energy consumption and improve the efficiency of electrical systems.