Any electrical or light pulse or frequency whether in a wire or fiber or wireless. The term is somewhat generic and may refer to virtually anything that is generated and transmitted (power, data, control signals). Although the term may be used by itself later on in a description or article, it is often used at least initially with another word, such as "carrier signal," "data signal" or "control signal." See signal-to-noise ratio and control signal.

Signal Vs. Signaling
A "signal" can refer to a data signal or a control signal, but "signaling" refers to transmitting only control signals. It is very common to hear the term in the telecom industry, where "signaling" means setting up and breaking down a call, but does not refer to the actual pulses or frequencies of the data (voice, text, etc.) itself (see SS7 and signaling).