A three-way switch allows you to turn lights or appliances on or off from two locations. Three-way switches are essential, especially for stairs or long hallways, so you can turn the lights on when you approach from one side. You can then turn off the lights when leaving from the other side of the hallway. A three-way switch is constructed differently than a normal switch. For starters, there is no particular on or off toggle. If both the buttons are up or both are down, the circuit is complete, and the light turns on. But, when both switches are in opposite directions, the course is open, and the light is off. The two terminals are either connected (as shown) or disconnected in a normal switch. When they are connected, the switch is "on." In a three-way switch, the top terminal connects to one of the bottom two terminals.