The (general) icosahedron is a 20-faced polyhedron (where icos- derives from the Greek word for "twenty" and -hedron comes
from the Indo-European word for "seat"). Examples illustrated above include
the decagonal dipyramid, elongated
triangular gyrobicupola (Johnson solid 
), elongated
triangular orthobicupola (
), gyroelongated
triangular cupola (
),
Jessen's orthogonal icosahedron,
metabiaugmented dodecahedron (
), nonagonal antiprism, parabiaugmented
dodecahedron (
),
18-gonal prism, 19-gonal pyramid, regular icosahedron, and rhombic
icosahedron.
The regular icosahedron (often simply called "the" icosahedron) is the regular polyhedron
and Platonic solid 
having 12 polyhedron vertices,
30 polyhedron edges, and 20 equivalent equilateral
triangle faces, 
.
