A potentiometer is common known as a "pot". They are normally used for controlling analogue signals, and acts as a variable resistor. Rarely are pots used for direct control of equipment requiring significant power.
A rheostat is a two-terminal variable resistor. Often these are designed to handle much higher voltage and current.
A switch is an electrical component used to interrupt or break an electrical circuit. Usually it allows a person to gain control of an electrical system or to control the power flow of a circuit.
