Relay is an electrical switch that opens and closes under control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered in a broad sense to be a form of electrical amplifier.

Relay racks are designed to handle most rack mount equipment needs. It has a 2-post aluminum or steel structure with either mounting holes or universal (square) mounting holes. These are also called 2-post racks or open bay racks. The vertical holes spacing on relay racks are standardized for mounting Telco, or computer/network equipment. The height of almost all rack mountable computer/network equipment products is standard rack units.

Relay sockets are made of metal or composite materials. These are available in a variety of shapes, sizes, and colors. It accepts relays, electromechanical switches in which the variation of current in one electric circuit controls the flow of electricity in another circuit. It differs in terms of terminal type, the number of pins per blade, and socket receptacle style.