Signal

noun
1.
anything that serves to indicate, warn, direct, command, or the like, as a light, a gesture, an act, etc.:
a traffic signal; a signal to leave.
2.
anything agreed upon or understood as the occasion for concerted action.
3.
an act, event, or the like that causes or incites some action:
The unjust execution was the signal for revolt.
4.
a token; indication.
5.
Electronics. an electrical quantity or effect, as current, voltage, or electromagnetic waves, that can be varied in such a way as to convey information.
6.
Cards. a play that reveals to one’s partner a wish that he or she continue or discontinue the suit led.
adjective
7.
serving as a signal; used in signaling:
a signal flag.
8.
unusual; notable; outstanding:
a signal exploit.
verb (used with object), signaled, signaling or (especially British) signalled, signalling.
9.
to make a signal to.
10.
to communicate or make known by a signal.
verb (used without object), signaled, signaling or (especially British) signalled, signalling.
11.
to make communication by a signal or signals.
noun
1.
any sign, gesture, token, etc, that serves to communicate information
2.
anything that acts as an incitement to action: the rise in prices was a signal for rebellion
3.

a variable parameter, such as a current or electromagnetic wave, by which information is conveyed through an electronic circuit, communications system, etc
the information so conveyed
(as modifier): signal strength, a signal generator

adjective
4.
distinguished or conspicuous
5.
used to give or act as a signal
verb -nals, -nalling, -nalled (US) -nals, -naling, -naled
6.
to communicate (a message, etc) to (a person)
signal
(sĭg’nəl)
A fluctuating quantity or impulse whose variations represent information. The amplitude or frequency of voltage, current, electric field strength, light, and sound can be varied as signals representing information.

language
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].
(1996-12-10)

operating system
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.
(1996-12-10)