Whiteside's Theorem is a concept in geometry that deals with the properties of convex polyhedra. It states that if a convex polyhedron has a certain number of faces, edges, and vertices, then these elements are related by a specific formula. This relationship helps in understanding the structure and classification of polyhedra. The theorem is named after Henry Whiteside, who contributed to the study of polyhedral geometry. It is often used in mathematical proofs and applications involving three-dimensional shapes, providing a foundational understanding of how these geometric figures are constructed and analyzed.