Reflection

The angle made with the normal of the surface and the ray is called the incident ray.

The angle formed by the reflected ray and the normal of the surface is the reflected rays.

$$\theta_i = \theta_r$$

Diffuse Reflection:

Light rays reflected from a rough surface.

Spectular Reflection:

Light rays reflected from a mirror.

Each reflected ray appears to come from a specific point called the image point as seen through dashed line.

Since our eyes and thus our brains can interpret rays that enter the eye as if they travelled in a straight lines.

This shows that if a mirror is positioned correctly, one only needs a mirror of half the length.