Icosahedron
In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes from Greek εἴκοσι (eíkosi), meaning "twenty", and ἕδρα (hédra), meaning "seat". The plural can be either "icosahedra" () or "icosahedrons".
There are many kinds of icosahedra, with some being more symmetrical than others.
The most well known is the regular convex or Platonic icosahedron.
Regular icosahedra
The most symmetrical are the two kinds of regular icosahedra, while the nonconvex form is called a great icosahedron. Each has 30 edges and 20 equilateral triangle faces with five meeting at each of its twelve vertices. Both have icosahedral symmetry.
Convex regular icosahedron
The convex regular icosahedron is the more common and is usually referred to simply as the regular icosahedron, one of the five regular Platonic solids, and is represented by its Schläfli symbol {3, 5}, containing 20 triangular faces, with 5 faces meeting around each vertex.
