An icosahedron is a solid figure of twenty faces, which is a polyhedron with twenty faces and twelve vertices. It is a regular polyhedron, meaning that all its faces are congruent and all its edges are the same length. It is also a Platonic solid, which is a three-dimensional shape composed of regular polygons. The icosahedron is one of the five Platonic solids, along with the tetrahedron, cube, octahedron, and dodecahedron.