A variable resistor is an electrical component that allows the resistance in a circuit to be adjusted. It is commonly used to control current flow and voltage levels in various devices. By changing its resistance, it can help regulate the brightness of lights, the speed of motors, or the volume of audio equipment. Variable resistors come in different forms, such as potentiometers and rheostats. A potentiometer typically has three terminals and is used for applications like adjusting sound levels in radios, while a rheostat usually has two terminals and is used for higher power applications. Both types are essential in electronic circuits for fine-tuning performance.