A rheostat is an electrical device used to control the flow of current in a circuit. It is similar to a RESISTOR, but it has a variable resistance that can be adjusted to control the amount of current flowing through the circuit. The term rheostat is derived from the Greek words 'rheo' meaning 'to flow' and 'statos' meaning 'FIXED'. Rheostats are commonly used in applications such as dimmer switches, motor speed control, and voltage regulation.