A relay switch is an electrical device that uses an electromagnet to control the opening and closing of a circuit. When an electric current flows through the coil of the relay, it creates a magnetic field that pulls a lever, either connecting or disconnecting the circuit. This allows a low-power signal to control a higher-power circuit, making it useful in various applications. Relay switches are commonly found in devices like home appliances, automotive systems, and industrial machinery. They help manage electrical loads safely and efficiently, enabling automation and remote control of devices without direct human intervention.