A shadow is a region of darkness where light is blocked.

A shadow occupies all the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light.

The closer to 90 degrees the angle between an elongated object and the direction of the light it blocks, the bigger its shadow.

The smaller the angle between the direction of the light and the surface on which the shadow occurs, the longer the shadow is.

If the object is close to the light source, the shadow is large. If the surface is curved there are further distortions.

For a non-point source of light, the shadow is divided into the umbra and penumbra. The wider the light source, the more blurred the shadow.

If there are multiple light sources there are multiple shadows, with overlapping parts darker, or a combination of colors. For a person or object touching the surface, like a person standing on the ground, or a pole in the ground, these converge at the point of touch.