In discussing only the color or diffuse aspect of light reflection (reflectance) in our materials, we have so far neglected to mention that surfaces often have physical properties that can cause light to reflect off them in a very different manner. This change in light behavior causes it of course to produce a very different visual result.
In computer graphics, the Lambertian model for diffuse reflection (reflectance) of light describes a perfectly uniform micro-faceted (or rough) surface that diffuses or scatters light equally in all directions. Whenever we discuss a surface in terms of its color alone, (what we might call a matte surface, for example) it is generally this kind of reflectance model that we have in mind.
Note
Lambertian reflectance is named after Johann Heinrich Lambert, who introduced the concept of perfect diffusion in his 1760 book Photometria, a publication that is in fact still available in paperback even today.
However...