The magnetic relay is a device used for controlling another circuit carrying a larger current. It consists of an electromagnet, a spring-loaded armature, and a set of contacts. When a current passes through the coil of the electromagnet, it generates a magnetic field which attracts the armature and causes it to move, closing or opening the contacts. This can be used to switch on or off a circuit carrying a larger current, or to switch between different circuits. The magnetic relay is commonly used in applications such as industrial automation, power systems, and telecommunications.