Why are three-way switches termed as such?

Three-way switches are termed as such because they allow for the control of a single light or set of lights from two different locations. This means that while you might have only two switches involved in controlling the light, there can be multiple configurations for lights that can be managed through these switches along with the addition of four-way switches if desired. The focus on the two locations of control (one for each switch) is critical to understanding the functionality of three-way switches.

The term does not refer to controlling lights from three locations, as that would typically involve a four-way switch in conjunction with two three-way switches. They do not inherently connect multiple circuits, and the use of three different colors of wire is not a defining characteristic of their function.