plural of traffic signal box

(US, Australia) Any of the large metal boxes containing traffic signal controls, found at roadsides and intersections, and often made available by the local council for artistic work.

(rail transport, British spelling) An electric railway signal with colour aspects, showing either red or green in a 2-aspect signal, with the addition of a yellow or double yellow aspect (meaning caution) in 3- and 4-aspect signals.

(rail transport, UK) A signal given to a train driver by the guard of the train, or a member of station staff, that the train is ready to depart.

(electronics, technology) The use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations.

(networking, telecommunications) A type of transmission technology in which signaling is separate from the data being transmitted, using one or more channels for transmitting data or voice information and one out-of-band channel for performing signaling functions.