a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day

A traffic light.

(electrical engineering) The ratio comparing signal power to noise power. / (by extension) The quantity of quality information compared to irrelevant or incorrect information.

A signal that only takes discrete values (contrasted to an analog signal that can take continuously varying values).

plural of analog signal

plural of digital signal

A signal that can vary in a continuous manner (as opposed to a digital signal that only takes discrete values).

(economics) A sign, attached to a commodity and concerning its price, that is intended to increase demand for it

(rail transport) A signal set at danger and showing a red light or other stop indication, which a train driver must not pass until it changes or until manually cleared past the signal by a dispatcher.

plural of danger signal