Signal:

1. any nonverbal action or gesture that encodes a message; "signals from the boat suddenly stopped"
2. an electric quantity (voltage or current or field strength) whose modulation represents coded information about the source from which it comes
3. In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying or spatial-varying quantity.
4. K&I: A voltage or current that, in some manner, is varied over time in order to encode and transmit information.
5. Conexions: Whether analog or digital, information is represented by the fundamental quantity in electrical engineering: the signal. Stated in mathematical terms, a signal is merely a function.