The Reflection Glossiness Render Channel stores the image's reflection glossiness as a grayscale image that represents the degree of Reflection Glossiness set for materials in the scene. White areas have the most reflection glossiness, while dark areas have little.
The amount of reflection glossiness for a material is set by its Reflection Glossiness parameter. For example, V-Ray Material (V-Ray Mtl) has a Reflection Glossiness parameter, and Fast SSS2 has a Specular Glossiness parameter that goes into the Reflection Glossiness render channel.
