Any illuminated object reflects part of the light shining on it but only the polished surface of a mirror can render a perfect reflection. The light rays from an actual object bounce off the mirror to give a virtual image. With a flat mirror, the real object and the virtual object are symmetric and appear to be at the same distance on either side of the plane of the mirror.
Symmetry rules at work in the reflection process explain how an image is formed by a plane mirror.
Object A (a teapot) can be moved around, illustrating the symmetry rules at work in the reflection of light rays.