The umbra, penumbra and antumbra are the names given to the three distinct parts of a shadow, created by any light source. For a point source only the umbra is cast. These names are usually used when referring to the shadows cast by celestial bodies.
Umbra The umbra (Latin: shadow) is the darkest part of a shadow. From within the umbra, the source of light is completely concealed by the occulting body. In astronomy, an observer in the umbra is said to be in the shadows experiencing total eclipse.
Penumbra The penumbra (Latin: paenes "almost, nearly" + umbra "shadow") the region in which only a portion of the occulting body is obscuring the light source. An observer in the penumbra experiences a partial eclipse.
Antumbra The antumbra is the region from which the occulting body appears entirely contained within the disc of the light source. If an observer in the antumbra moves closer to the light source, the apparent size of the occulting body increases until it causes a full umbra. An observer in this region experiences an annular eclipse.