An image that is laterally inverted means is inverted from left to right, like an image seen in a mirror. The right side of the object appears as its left side, and vice versa.
If a person looks into a mirror and raises his right hand, the image in the mirror makes it look like the person raised his left hand due to lateral inversion. Although it appears that mirrors reverse images, they actually switch them from back to front in the same way that a printing press does. The image seen in the mirror is a light-print, not an actual reflection. This is caused by light reflecting off of the mirror's surface. Mirrors have a smooth surface that reflects light without disturbing images. This is known as specular reflection.