...? All three except the circle are polygons, even though the star isn't a convex polygon.
Also, I love this section from that article:
Things to do with polygons * Cut up a piece of paper into polygons, and put them back together as a tangram.
* Join many edge-to-edge as a tiling or tessellation.
* Join several edge-to-edge and fold them all up so there are no gaps, to make a three-dimensional polyhedron.
* Join many edge-to-edge, folding them into a crinkly thing called an infinite polyhedron.
* Use computer-generated polygons to build up a three-dimensional world full of monsters, theme parks, aeroplanes or anything - see Polygons in computer graphics below..