Smooth surfaces such as clean glass, reflect light back to the observer in parallel rays, which is called regular reflection. Surfaces that are not smooth reflect light to the observer in many different directions, which is called diffuse reflection.
See also laws of reflection.
In mathematics, reflection is a way of transforming a shape in the same way that a mirror does. The reflection of a shape in a mirror line is an identical shape that has been flipped over. When an object is placed a certain distance in front of a mirror, its image in the mirror appears the same distance away from edge of the mirror. Likewise, all the points on a shape and all the points on its image are same distance away from the mirror line.
See also transformation