A SPDT switch is a type of switch that can be used to switch between two different circuits or sources of power. It stands for Single Pole Double Throw. In a SPDT switch, there is one pole (or lever) and two throws. The pole has two positions. When it's in one position the power goes to one of the throws and in the other position the power goes to the other throw. It's like a light switch in your house - when you flip it one way the lights are on and when you flip it the other way the lights are off.