In geometry, a dodecahedron (Greek δωδεκάεδρον, from δώδεκα 'twelve' + ἕδρα 'base', 'seat' or 'face') is any polyhedron with twelve flat faces, but usually a regular dodecahedron is meant: a Platonic solid. It is composed of 12 regularpentagonal faces, with three meeting at each vertex, and is represented by the Schläfli symbol {5,3}. It has 20 vertices and 30 edges. Its dual polyhedron is the icosahedron, with Schläfli symbol {3,5}.

A large number of other (nonregular) polyhedra also have 12 sides, but are given other names. Other dodecahedrons include the hexagonal bipyramid and the rhombic dodecahedron.

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