A relay is a quick or real electric switch that opens and closes by directing another electrical circuit.
The method of controlling the opening and closing of this electric key is in various forms of mechanical, thermal, magnetic, electrostatic and …. The relay was invented by Joseph Henry in 1835.
Since the relay can drive a stronger current than the input current, it can also be considered a booster in the broader sense.
In the past, the relays were usually made with a winding and used the current to generate the magnetic field and open and close the circuit. Today, many relays are made in solid form and do not have moving parts.