Also called a single pole double throw switch, a changeover switch has a single input and can connect to and switch between two outputs. This means it has one input terminal and two output terminals.
A single pole double throw switch can serve a variety of functions in a circuit. It can serve as an on-off switch or connect circuits to any two various paths that a circuit may need to function in. For example, a SPDT switch can connect to create a ready mode and a standby mode in a printer. It can also can be used to turn a green light on in one switch position, or a green light in the opposite switch position.