Comment by Daub

I teach 3D modelling and rendering and also drawing and oil painting.

Many time in my traditional media classes I will use the term ambient occlusion (AO) and describe it in exactly the same way as I would to my 3D class. Specifically, I ask them to imagine being surrounded by a sphere of even light. In such a case, where would the shadows be? I follow this by discussing contact shadow (e.g. the dark line between your hands as they are placed together) and core shadow (e.g. the darkness of your nostrils). In 3D rendering, both these classes of shadows are served by the AO pass.

Certainly, I would say that AO is a natural phenomenon, but it is also an effect that can be used to sweeten the naturally flat effect of a raster engine like Eevee.