Definition:Icosahedron/Regular

Definition
A regular icosahedron is an icosahedron whose $20$ faces are all congruent equilateral triangles.

The regular icosahedron is an example of a deltahedron.

Also known as
It is commonplace for authors to refer to a regular icosahedron as just an icosahedron, glossing over the fact of its regularity.

Also see

 * Definition:Platonic Solid
 * Definition:Deltahedron