A polygon is regular if all the sides are congruent with each other and all the angles are the same size. A solid however is regular if each side is a regular polygon and congruent to each other and all the dihedral angles formed by the sides are the same size.

While there is **an infinite number of regular polygons** (triangle, square, pentagon, hexagon,…), there are **only 5 regular solids** (called platonic as already known to the ancient Greeks): tetrahedron, octahedron, cube, icosahedron, dodecahedron.