Back in the old comic book days, the act of drawing darker parts of a person or object to indicate lighting or shadows was called “shading”. The name stuck beca

Back in the old comic book days, the act of drawing darker parts of a person or object to indicate lighting or shadows was called “shading”. The name stuck because the first shaders were focused on that. Later, these GPU programs were used for other things, leading to somewhat nonsensical-sounding terms like “vertex shader”. But yeah, that’s why they were originally called that: they shaded the dark parts of an image.