Generally, all objects reflect light. How the object reflects light determines its reflectivity. Smooth surfaces reflect light at the same angle that the light falls on them. This is known as the angle of reflectance. Textured or unsmooth surfaces tend to be less predictable in how they reflect light. This becomes important in photography since you must always be aware of reflections resulting from your lighting equipment.
Be cautious when photographing smooth subjects that light is not being directed off of them and onto other parts of the scene. In addition, you must consider that some light from the source will be reflecting off of the subject and into the camera. This reflection will appear as the mirror image of your light source in the surface of the object. A catchlight is an example of this reflection.
Typically a diffused light source will have a softer, more subtle reflection in the surface of an object. This is one reason on-camera flash (which is not diffused) can cause unattractive reflections in shiny surfaces. Commercial photo studios frequently use softboxes or other diffusion modifiers when photographing shiny objects to keep the reflection from becoming a distraction in the final image.