Polygon
A polygon is a closed two-dimensional figure bounded by three or more straight line segments. The segments are called its edges or sides, and the points where two edges meet are the polygon's vertices.
Example
A regular hexagon is a polygon with $n = 6$ equal sides and $6$ equal interior angles. The sum of its interior angles is calculated as $(n - 2) \times 180^\circ = 720^\circ$.