The shape is taken directly from Albrecht Dürer's etching Melencolia I. The origin and meaning of it have never been completely retraced, but multiple theories have been formed, many of which are based on the appearance of the solid in the etching. (Schreiber's interpretation seems most likely to me, unless certain derived numbers turn out to have a symbolic meaning in alchemical or humoralistic theories.)
Also known as "Dürer's solid", it is a truncated rhombohedron (or truncated triangular trapezohedron). To recreate it, one takes a cube, and elongates and truncates two diagonally opposite vertices.