Digital signals

Signal is defined as a function of dependent variables of independent varisbles
Or
Signal is a  quantity which carries the information
The independent variables are Time, Distance and etc
Signal can be one dimensional or two dimensional or many dimensional.
Signal can devide as ANALOGUE SIGNAL and DIGITAL SIGNAL.
Again Analogue signal divided as CONTINUOUS TIME SIGNALS and DISCRETE TIME SIGNALS
Note
All continuous signals are Analogue signals buy all Analogue signals are not continous signals