Octadecagram

The octadecagram, or odge, is a non-convex polygon with 18 sides. It's created by taking the fourth stellation of an octadecagon. A regular octadecagram has equal sides and equal angles.

It is one of two regular 18-sided star polygons, the other being the great octadecagram.

It is the uniform quasitruncation of the great enneagram.