Specular and Diffuse Reflection
Specular Reflection - if a material surface is microscopically 
smooth and flat, such as float glass the incident and reflected light rays make the same angle with a normal to the reflecting surface producing specular reflection.
Diffuse Reflection - if a material has a 'rough' surface, not 
microscopically smooth, diffuse reflections will
occur. Each ray of light falling on a small particle of the surface will obey the basic law of reflection but as the particles are randomly oriented, the reflections will be< randomly distributed. A perfect diffusely reflecting surface would in practice reflect light equally in all directions, giving a perfect matt finish.
Patterened or finely etched glass surfaces produce significant diffuse reflections.