At its core, a relay is a device that allows a low-power electrical signal to control a higher-power circuit, thereby serving as an intermediary switch. This capability is invaluable in environments where the control circuit must operate with minimal power, while still controlling significant electrical loads. For instance, in industrial automation, relays are used to activate machinery, regulate power supplies, and monitor system status without the need for manual intervention. They are also found in various consumer electronics, automotive systems, and even in advanced applications like robotics and smart grids.