A relay is an electrically operated switch that allows one circuit to control another circuit without a direct physical connection. It uses an electromagnet: when current flows through the coil, it generates a magnetic field that moves a switch to open or close another circuit. This allows a low-power signal to control a higher-power circuit safely and efficiently.

Relays are used in many applications, including automotive systems, industrial machinery, home appliances, and electronic circuits. They can turn devices on or off, control motors, route signals, or protect circuits from overloads.

In simple terms, a relay is like a remote-controlled switch that enables one part of a circuit to control another safely.