Question:What is meant by a digital signal?
Digital signals only take on two values.
These are On (represented by the number 1) or Off (represneted by the number 0).
By 'on' and 'off' we literally mean that whatever medium is being used to transmit the signal (light, sound, voltage) is being turned on and off repeatedly to form a pattern of flashes that make a code.
Remember: All signals require a code to be agreed between sender and reciever so that the signal will be understood.