Flat shading
One lighting value per polygon — the whole triangle gets a single colour and the surface looks faceted.
The cheapest shading model: compute the light once from the face normal and fill the entire triangle with the result. You get visible facets, because neighbouring polygons never blend at the shared edge. Gouraud (per vertex, interpolated) and Phong (per pixel) smooth that out at a higher cost.
Flat shading ruled early real-time 3D where every cycle counted — Star Fox (1993) and the flat polygons of arcade hardware. Today it is as often a style choice as a saving: the angular look has become an aesthetic in its own right.