A star-shaped polygon (n-gram) is a non-convex regular polygon. To build it starting from a regular n-polygon like a pentagon (n = 5), hexagon (n = 6), etc., follow these steps:
Prolong the sides of the starting polygon.
Extend each side until it intersects the prolongation of the next non-adjacent side.
For odd-sided polygons, you can have an intersection between prolongations separated by an increasing number of sides: check all the possibilities! Read more