What is any undesired change in a signal from input to output?

The concept of undesired changes in a signal from input to output refers specifically to the alteration of the signal's original characteristics. Distortion is characterized by any change in the shape or form of the waveform, which can affect the fidelity of the signal. This can include alterations in amplitude, frequency, or phase that do not correspond to the intended output. Distortion can occur due to various reasons including non-linearities in the system or interference during transmission, leading to an output that doesn't accurately represent the intended input signal.

In contrast, while noise and interference also relate to unwanted changes, they typically refer to additional signals that can either mix with the original signal or obscure it, rather than changing its inherent shape. Deviation generally describes a divergence from a standard or expected value but does not specifically address the waveform alterations encompassed by distortion. Thus, distortion most precisely defines an undesired change affecting the signal’s form and integrity from input to output.