Polygons

A polygon is a closed two-dimensional shape. It is a simple curve that is made up of straight line segments called edges. It usually has at least three sides and three corners, called vertices, or more. It could also be referred to as 'A closed plane figure bound by three or more straight line segments'. A square is a type of polygon with four edges. The smallest possible polygon in a Euclidean geometry or "flat geometry" is the triangle, but on a sphere, there can be a digon and a henagon. If the edges of the polygon do not cross each other, the polygon is called simple, otherwise it is complex. In computer graphics, polygons (especially triangles) are often used to make graphics.
(care of simple.wikipedia.org)

Properties of Regular Polygons

Number of sides	Name	Order of Rotational Symmetry	Number of lines of Reflective Symmetry	Total Interior Angles /°	Interior Angles /°	Exterior Angle /°
3	Equilateral Triangle	3^rd	3	180	60	120
4	Square	4^th	4	360	90	90
5	Regular Pentagon	5^th	5	540	108	72
$n$	$n$ -sided regular polygon	$n^{th}$	$n$	$180 (n - 2)$	$180 (1 - \frac{2}{n})$	$\frac{360}{n}$