Specular maps in Second Life are texture layers that convey additional rendering information to the graphics engine. This additional information is used in conjunction with standard “diffuse” textures to add a whole new level of detail to otherwise flat surfaces.
I’ve made a couple of tops with Specular maps. With the first one (below) I tried to make a satin cloth, but it looks more like plastic. That can be seen as nice if you are into that sort of thing. The second attempt (above) came out better. Less plastic appearance and the design had a nice sheen when viewed in the light.