1 In networking, a means of passing information between two or more networks, each offering a similar network function but each using a different protocol. In general a relay differs from a gateway or bridge in offering a store-and-forward service rather than a real-time service. As an example, a mail relay may be used to pass mail messages between networks using different mail protocols. See also cell relay, frame relay.
The term relay is used in some communities as synonymous with bridge or gateway. These three terms have meanings that vary between different communities at the same time, and within a given community at different times.
2 An electrically controlled switch enabling small signals to control much larger powers than would normally be possible as well as providing isolation between circuits. Various contact arrangements, e.g. normally open, normally closed, change-over and multiple poles, are available, as are bistable versions.