Specular gloss map
From polycount
Specular Gloss Map
A texture that controls the width/power of the specular highlights from real-time lights.
This usually only requires a monochrome texture. If the shader supports RGB the gloss map can be used to control a separate width/power for each color, useful for surfaces that have more complex reflective properties like metals, beetle shells, etc.
Usually a shader will also support per-pixel control for the color/intensity of the specular highlights (see Specular color map).