What is the difference between a polyhedron and a non-polyhedron?

A polyhedron is a three-dimensional geometric shape with flat polygonal faces, straight edges, and vertices, such as cubes and pyramids. In contrast, a non-polyhedron includes shapes that do not fit this definition, such as spheres, cylinders, and cones, which have curved surfaces and do not consist entirely of flat faces. Essentially, the key difference lies in the presence of flat polygonal faces in polyhedra versus the curved surfaces in non-polyhedra.