A 4-way switch is a type of switch used in combination with 3-way switches to control lighting from three or more locations. It is not used on its own, but in addition to a combination of switches. A 3-way switch connects traveler wires from that switch to one side of the 4-way switch, while the other side is connected to the other 3-way switch, and the 3-way switch is then connected to a light. When connected properly, a simple flip of any of the switches will turn on the light. A 4-way switch has four terminals that provide two sets of toggle positions. Each set of terminals is one of the toggle positions. When the switch is in the up position, the current can flow through two terminals. In the down position, the current flows through the other two terminals. The 4-way switch is simply crossing the connections, or connecting them straight through, sort of an XOR function.