A specular reflection or gloss is what you get from a polished surface or mirror. It is clear, and you can see "through" the mirror. A diffuse...

A specular reflection or gloss is what you get from a polished surface or mirror. It is clear, and you can see "through" the mirror. A diffuse reflection is what you get from a white wall. The light is bounced off it, but in random directions, so you cannot see the light source in the reflection. Many surfaces will be a mix of specular and diffuse - e.g. a smooth desktop will give both kinds of reflection. A polished surface gives more specular reflection and less diffuse reflection.