The highlights on objects are reflections of the light source. Even on the roughest surface a highlight (and therefore, a reflection) will appear, although we generally think of reflections as occurring mainly on smooth surfaces.
A reflection is a replication of the light source or the brightly lit part of an object on another surface, How clear this replication is and how sharply focused its edge will tell us how smooth the reflecting surface is. A reflection whose edge is soft and out of focus indicates a rougher surface than does a reflection whose edge is sharply focused. If the reflecting surface is extremely rough, the edges of reflections in it will be so out of focus that all characteristics of whatever is reflected are lost.
In drawing, reflections are useful in describing polished surfaces, water, metallic objects, and transparent objects.
Highlights on objects are reflections. Although we usually think of reflections as appearing on smooth surfaces, they do appear on rough surfaces as well, but in unfocused form. Here, the light area on the tennis ball (left) is an unfocused reflection. The edges of a highlight tell us visually how smooth or rough an object is. Because the reflection on the seven ball (center) is less focused than the one on the Christmas ornament, we know the ornament has a microscopically smoother surface.