an action, gesture, word, etc event, or watchword that has an been agreed meaning, e.g. to begin on as the occasion for a concerted action
the signal to attack
anything that prompts a particular action or event to take place
a conventional sign, sound, etc that conveys a particular piece of information or gives a warning or command
a sign, e.g. consisting of a set of coloured lights, or a vertical post with a moving arm that regulates the flow of traffic, esp on a railway line
the sound or image conveyed by telegraph, telephone, radio, radar, or television
the variations of a physical quantity, e.g. pressure, current, or voltage, by which information may be transmitted in an electronic circuit or system, e.g.:
the wave that is used to modulate a carrier (wave carrying information to be transmitted)
the video signal
the wave produced by the modulation of a carrier by a signal
a radio signal