Why does graphics speak of "dielectrics" rather than insulators? For example, Filament's documentation at https://google.github.io/filament/Filament.md.html uses the term "dielectrics" when contrasting nonconductors to conductors, which it calls "metallics". And here on stackexchange, https://computergraphics.stackexchange.com/search?page=2&amp;tab=Relevance&amp;q=dielectric also produces many hits for "dielectric". I would have normally expected the word "insulator" in these instances. Does "dielectric" stem from some historical source, or is it the accurate term to use?
Strictly speaking, dielectrics are not necessarily insulators. For example, salt water is a reasonable conductor but also a dielectric.

The term "dielectric" tends to show up in discussion of the Fresnel effect—how reflectance and transmittance vary with angle. Dielectric materials (i.e. nonmetals) are contrasted with metallic materials as they have different Fresnel behavior, which can be traced back to how the materials react on a microscopic scale to the electromagnetic field of an incident light wave.

So, for computer graphics purposes, the axis "dielectric/metallic" is more relevant than that of "insulator/conductor", since the former directly affects the appearance of materials.