signal (redirected from Colour signal lights)

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).

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1.	(language)	SIGNAL - A synchronous language by Le Guernic et al of INRIA. ["SIGNAL - A Data Flow-Oriented Language for Signal Processing," P. le Guernic, IEEE Trans Acoustics Speech & Signal Proc, ASSP-34(2):362-1986-04-374].
2.	(operating system)	signal - A predefined message sent between two Unix processes or from the kernel to a process. Signals communicate the occurrence of unexpected external events such as the forced termination of a process by the user. Each signal has a unique number associated with it and each process has a signal handler set for each signal. Signals can be sent using the kill system call.