• A device in which a variation in a parameter, such as capacitance, current, frequency, or voltage, controls a component, circuit, another device, piece of equipment, system, or mechanism. A common example is a device in which a varying current or voltage controls the contacts which make or break a circuit. Relays may be electrical, electronic, electromechanical, electromagnetic, photoelectric, and so on, and there are numerous types, including armature, capacitance, current, reed, and frequency. In addition, relays may be classified as automatic, bi-directional, bistable, delay, differential, directional, high-speed, latching, and the like.
  • A relay (1) used as a switch.
  • In communications, a device that repeats, retransmits, or otherwise passes on a signal. Also, to pass on a signal utilizing such a device.

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