A space-filling polyhedron is a three-dimensional shape with polygonal faces that will tile three-dimensional space without leaving gaps. The simplest example is a cube, which is the polyhedron commonly used for d6 dice. The Dice Lab d8 (truncated octahedron) and d12 (rhombic dodecahedron) dice are also space fillers, as shown below.
Truncated Octahedral d8
Rhombic Dodecahedral d12