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Umbra and penumbra from an extended source
You may have noticed that shadows are often fuzzy, particularly when the surface on which the shadow lies is far from the object casting the shadow. This fuzziness is because no light source is only a point in space. All sources have some geometrical size. Thus, light from one edge of the source is not quite parallel to light from the other edge.

The evenly dark part of a shadow is called the umbra. Umbra means 'shade' in Latin. The fuzzy part between the dark and the light is called the penumbra. Pene means 'almost' in Latin. If one is in the umbra of an object, the light source is completely obscured. If one is in the penumbra, the source is only partially obscured, to a greater or lesser degree as one moves through the penumbra.

The umbra of a shadow is not absolutely black because there is always scattered light that makes its way into it. In the case of sunlight, the scattered light is mostly bluish sky light, so shadows are bluer than normal.