Polygon

Polygon, closed plane figure bounded by three or more straight lines, such as triangles (3 sides), pentagons (5 sides), and dodecagons (12 sides). Convex polygons have interior angles that are all either acute or obtuse; in concave polygons one or more of these angles is reflex. A polygon with equal angles and sides equal in length is called a regular polygon. A spherical polygon is a closed figure on the surface of a sphere bounded by arcs of great circles.