A polydecahedron is a type of polyhedron characterized by having a large number of faces, specifically more than twelve. The term is not widely used in geometry and often refers to complex, multi-faceted shapes that can have various geometric properties. Polydecahedra can be regular, semi-regular, or irregular, depending on the arrangement and types of their faces. However, they are not as commonly studied or defined as more familiar polyhedra like cubes or dodecahedra.