The most familiar light switch, the common basic switch, is referred to by hardware dealers and electricians as a “single-pole switch.” With a single-pole light switch, flipping the lever up completes the circuit, turning lights or appliances on, and flipping it down breaks the circuit, turning lights or receptacles off. A single-pole switch has two brass terminal screws on the side.

There are places where you want to be able to control a light—or a series of lights—from more than one location. Three-way switches (shown below and below left), traditionally used at each end of a stairway or hallway, are the answer. A three-way switch has three terminal screws, may have a green grounding screw, and has no "on" or "off" markings on the toggle.

Three-way dimmers will work in those same places. A standard three-way dimming control can be mounted at one end of the hallway or staircase, or a special two-location dimming control is able to dim from either end of the hall or stair.

Four-way on/off switches (shown at right) may be combined with three-way dimmers or switches when you want control of lights from three or more different locations. A four-way switch has four terminals, may have a green grounding screw, and has no markings on the toggle.