A Solid State Relay (SSR) is an electronic switching device that performs the same function as a mechanical relay but uses semiconductor components to control the flow of electrical current. Unlike traditional relays, which rely on electromagnetic coils and moving contacts, SSRs use components like TRIACs (Triode for Alternating Current) or MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors) to switch the circuit on or off. These components are controlled by a low-voltage input signal, making SSRs highly efficient and reliable in controlling high-voltage or high-current loads.