What does Ra mean by 'distortion'

[Asolsutsesvyl]

Here's the technical signal processing view.

A pure tone (sine wave) is just one frequency.

There's many types of distortion, depending on the context. Contexts include amplitude, frequency, phase, shape of the waveform, etc. Distortion can create a different frequency spectrum, usually richer - unless you count simply shifting the frequency or the amplitude as a type of distortion. Ra seems to refer to a complication of what is more fundamentally there when using the word, meaning distortion in general which creates more frequencies without shifting the base frequency, and that brings to mind the below.

Deforming the shape of the waveform creates a richer spectrum, mainly by adding more frequencies related to those already there. Amplitude, frequency, or phase can be modulated, for more complex patterns of richer frequencies created from simple beginnings, and this is for example the basis of the 80's "FM synthesizer" sound.