Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. n geometry, a decagram is a 10-sided star polygon. There is one regular decagram star polygon, {10/3}, containing the vertices of a regular decagon, but connected by every third point. There are two regular decagram star figures: {10/2} and {10/4}, connected by every second and every fourth point respectively. A star polygon is a non-convex polygon which looks in some way like a star. Only the regular ones have been studied in any depth; star polygons in general appear not to have been formally defined. They should not be confused with star domains.