What is a relay?

A relay is an electromechanical or solid-state device that acts as a switch. However, instead of being toggled by a human finger, it is toggled by an electrical signal. In a standard mechanical relay, a small electrical current energizes an electromagnet, which physically pulls a set of switch contacts open or closed. This allows a low-power circuit to safely control a high-power circuit without direct electrical connection between the two. The other options describe active components like transistors or operational amplifiers, which manipulate and amplify electronic signals rather than mechanically switching a path open or closed.