A rheostat is an adjustable resistor that is used to vary the amount of current flowing through a circuit. It is typically made up of a resistive wire or coil, a rotary or sliding contact, and a supporting structure.

By changing the position of the contract, the amount of resistance in the circuit can be varied, which in turn controls the current flow. Rheostats are often used in electrical experiments and electronic circuits to control the intensity of light or the speed of a motor, among other applications.