What is the difference between regular and semi-regular polyhedra? Actually, what in the world are polyhedra? Many students are not familiar with this unique math term and what it means. In schools the concept of polyhedra is taught to the students beginning in middle school. The simple definition of “polyhedron” given in middle school is a three-dimensional solid with faces that are all flat. In schools, the lessons are vague about the specifics of regular and semi-regular polyhedra. Regular and semi-regular polyhedra are also referred to as the Platonic solids and Archimedean solids. The question that always pops up when discussing polyhedra is, "Why are not all 3-dimensional figures a part of the Platonic or Archimedean groups of solids?" This website explores the answers to these questions, including the history of polyhedra, an explanation of the mathematics behind polyhedra, and their significance in the world of mathematics.