An indicator, such as a gesture or colored light, that serves as a means of communication. See Synonyms at gesture. A message communicated by such means. Something that incites action: The peace treaty was the signal for celebration. Electronics An impulse or a fluctuating electric quantity, such as voltage, current, or electric field strength, whose variations represent coded information. The sound, image, or message transmitted or received in telegraphy, telephony, radio, television, or radar. Notably out of the ordinary: a signal feat; a signal event. To make a signal to: I signaled the driver to proceed. To relate or make known by signals: They have signaled their willingness to negotiate. To make a signal or signals.