Polygon : A polygon is a two-dimensional shape which has a boundary with $N\geq 3$ corners $C_1, C_2,\ldots C_N$ and edges equal to the line segments $C_1C_2$, $C_2C_3$,..., $C_{N-1}C_{N}$ and $C_NC_1.$ Triangles, quadrilaterals and octagons are all examples of polygons.