Flat Shapes

So, I knew that dihedral groups were groups that described symmetries of polygons, but never knew why they were called that.

So apparently, 2-D polygons are called dihedrons because they have two faces if you imagine them in 3 or higher dimensional space.

And you also have symmetries of tetrahedral, octahedral groups etc., that describe the symmetries of 4,8 faced polehedrons!