There are two major types of mirrors. One is the flat mirror, and the other is curved mirror. And below are the differences between them.

Flat mirror is also known as plane mirror. Sine flat /plant mirror is a smooth surface, specular reflection will occur when light comes by, which means the angle of incidence equals the angle of reflection from the normal line. When the eyes receive these light from the mirror, it seems that the object is behind the mirror. This type of image actually not real and it's called a virtual image. It is virtual because light waves do not actually pass through that point, and we can only see it but not touch it. The distance between mirro and the object is called object distance and the distance between the virtual image and mirror is image distance. In flat mirror, object distance equals to image distance, and that is why in geometry we have the term mirror symmetry.

For curved mirror there are two types of them -- concave mirror and convex mirror. A curved mirror that has its center closer to incoming light than its edges is called a convex mirror while one that has its center further away from incoming light than its edges is called a concave mirror. Generally we assume that light waves reachng the lens come from an object infinitely far away and so the light waves will be parallel with the principal axis. We can distinct these two types of curved mirror this way: Concave mirror can converge light, while convex mirror diverge light. What other characteristics do they have?

The focal point of both the concave and convex mirrors are (1/2) * R away from mirror. For a concave mirror a real image is formed at the focal point outside the mirror while for a convex mirror a virtual image is formed at the focal point behind the mirror. Concave mirror is often seen at solar water boiler becuase light is converged/focus so the energy at one point is high enough to boil water. We often see convex mirror in parking lots because convex mirror diverge light and help to attain a wider view than flat mirror.