Final answer:
The two most common types of variable resistors are potentiometers and rheostats, which are used in electronic circuits to vary resistance and thereby control voltage or current.
Step-by-step explanation:
The two most common types of variable resistors in electronics are the potentiometer and the rheostat. A potentiometer is a three-terminal device used to vary the resistance in a circuit, effectively adjusting the voltage or current. It typically consists of a resistive track with a wiper that slides along the track to change the resistance value. A rheostat, on the other hand, is similar but usually has only two terminals (one connected to the end of a resistive track and the other to the variable wiper). It adjusts the current flow in the circuit by changing the resistance. These components are crucial in circuits that require the ability to adjust the level of resistance dynamically, such as in volume controls, dimming lights, and tuning circuits.