How did a 'three-way switch' get its name?

Answer 1

"How does a single pole switch differ from a three way?" is a trick question often asked to catch-out new trainee electricians because the common but mis-named "three-way switch" is actually a single pole, double throw switch, i.e. it is only a 2-way switch, not a 3-way switch.

A pair of "3-terminal, single pole, double throw" switches are often used to hook-up two separate light switches to control one light or one set of lights.

A proper "3-way switch" would be capable of being switched to 3 different positions and could have one, two or more poles. Each pole could be either single- or double-throw.

The same answer put in a different way

Despite the fact that the name "3-way switch" is often used to describe it, if it is of the type that has just one pole that can only be physically switched 2 ways, the name "3-way switch" is quite wrong for that particular switch. A "3-terminal, single pole, double throw" switch" is a more accurate description for it.

Comment

'Three-way switch' -American term. 'Two-way switch' -UK term for the same type of switch. Used to operate a lamp from two different locations.