A signal is defined as a function of one or more variables, which provides information on the nature of a physical phenomenon.
When the function depends on a single variable, the signal is said to be one-dimensional, for example, a speech signal whose amplitude varies with time, depending on the spoken word and who speaks it.
When the function depends on two or more variables, the signal is said to be multidimensional, for example, an image (2-D signal).
A system is an entity that takes an input signal and produces an output signal. It is a combination and interconnection of several components to perform a desired task.
The system responds to one or more input quantities, called input signals or excitation, to produce one or more output quantities, called output signals or response.
Block diagram representation of a system