Two three-way switches are used where you want to be able to turn a light off or on from two locations, such as at each end of a hallway or stair.
A three-way switch has three terminal screws, may have a green grounding screw
and has and no "On" or "Off" markings on the toggle.
A four-way switch has four terminals, may have a green grounding screw and has no markings on the toggle. It's combined with three-way switches to control lights from three or more different locations.
Related terms: 3 way and 4 way switches, how a 3 way light switch works, how three way light switches work, how four 4 way electrical switch works, three four way switch wiring diagrams
Two three-way switches are used where you want to be able to turn a light off or on from two locations, such as at each end of a hallway or stair.
