Relay
A relay is a switch that is opened or closed by an electromagnet instead of by hand. A small current through its coil pulls a metal contact into place, which lets a low-power circuit turn a high-power circuit on or off. Because the coil stores energy in its magnetic field, it can produce a voltage spike when switched off.
Example: The click you hear when a car's turn signal or headlights come on is often a relay switching.