Electrical switches are designed to either allow or stop current from travelling through a circuit. In the case of single- and double-pole switches, they are created in the form of a toggle switch, which has an on and an off setting. Single- and double-pole switches look very similar but have a different number of terminal screws to attach the wires.
The term "pole" refers to the number of circuits that are controlled by a switch, meaning that a single-pole switch controls one circuit, and a double-pole switch controls two circuits (through the flipping of one toggle switch).
The single-pole switch is the most basic (and most used) form of light switch, used to turn a light on and off from one location. The switch has an on and off markings, with the toggle being pushed up to turn the light on, and pushed down to turn the light off.
The single-pole switch has two terminal screws, with the hot black wire connecting to one terminal, and the outgoing black wire to the other terminal -- these switches can come with, or without, a ground terminal screw. The white neutral wires do not connect to the switch, but are joined together with a wire nut.
Double-Pole Switches and Wiring
The double-pole light switch also has on and off markings, and like the single-pole also turns off lights from a single location. However, this switch has four terminal screws used to connect a 240-volt circuit (two 120-volt circuits that share a common white wire), and always has a ground terminal screw. Its connection process is the same as connecting two single-pole switches separately.