jocose: That's not exactly right. :\ That is a 2d art tutorial. In 3d: Specular maps define the brightness/color of a highlight. Gloss maps define the size of a highlight.
just to clarify something: Glossyness is a measure of how much light is scattered when it bounces off a surface. Super smooth things like polished metal/ wood/plastics have a high gloss value as they are so smooth. unfinished concrete, metal, un varnished wood have a pretty low glossyness becuase they are rough and scatter…