The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction, for a collimated beam (such as a point source) of light, only the umbra is cast.
A triptych is a work of art (usually a panel painting) that is divided into three sections, or three carved panels that are hinged together and can be folded. Hope this helped :)
