A Solid State Relay (SSR) is an electronic switching device that serves a similar function to an electromechanical relay. SSRs differ significantly in their design and operation.
SSRs do not have any moving parts such as contacts, armatures, or springs. Instead, they rely on solid-state electronics. When an external voltage (AC or DC) is applied across its control terminals, an SSR can switch on or off. This switching action occurs without any physical movement.