relay

A relay is an electromechanical or electronic switch that uses a control signal to operate a pair of contacts, opening or closing a circuit. Relays provide electrical isolation between the control circuit and the load circuit and enable a low-power signal to switch high-power devices.

The most common form is the electromagnetic relay, with a coil, an armature, and fixed contacts. Energizing the coil generates a magnetic field that attracts the armature and moves the contacts. Solid-state relays substitute transistors or thyristors for moving parts, offering silent operation and longer life in some applications.

Relays are used in automation, control systems, automotive electronics, and safety circuits to control motors, lights, and other equipment. They are rated by coil voltage, contact configuration (for example, single-pole double-throw), and current/voltage capacity. Mechanical relays have finite life due to contact wear; solid-state relays have no moving parts but introduce on-state resistance and leakage currents.

In athletics, a relay is a team running event in which runners pass a baton within designated zones. Common events include 4x100 and 4x400 meters. Strategy focuses on baton handling, speed, and order of runners; a dropped baton or early handoff can disqualify the team.

In communications and networking, a relay or relay server forwards messages or traffic between endpoints, serving as an intermediary. In telecommunications, relay stations extend the reach of networks, repeating signals to cover greater distances.

In biology, a relay describes a neuron or neural pathway that passes a signal from one region to another, forming part of sensory, motor, or reflex circuits.