Signals are sets of data or information.

One-dimensional signals include single-variable functions, such as the variations in air pressure over time in human speech.

Multi-dimensional signals are those that function based on two or more variables. An example is a monochromatic image that measures light intensity according to the horizontal and vertical positioning.

Systems are collections of devices that process input signals into one or more output signals.

Systems can be classified as single-input, single-output, or multi-input or  multi-output.

Systems can vary widely, encompassing things like electrical systems, mechanical systems, computer programs, and the human body.

The resistor-capacitor network is a simple system with a source voltage as the input and the capacitor voltage as the output.

The human body, a complex system, responds to heat exposure on a fingertip by sending signals from the nerve ending the finger to the central nervous system. This system then produces multiple output signals instructing various muscles in the arm to retract the finger.

Mathematical modeling of signals and systems facilitates the development of systems to execute specific operations.