Electronic components that perform switching control of electrical circuits using electromagnetic force. Used in control panels of manufacturing equipment, automation systems, and NC machine control circuits to safely switch high-power circuits with low-power control signals. Various types include electromagnetic relays, solid state relays (SSR), timer relays, and counter relays, selected based on contact capacity, operating voltage, and response speed. Unlike mechanical switches, remote control is possible, and complex control logic can be built in combination with PLCs and sequencers. Industrial applications require high reliability and long life, using products with excellent vibration, temperature, and noise resistance.