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In geometry, a polygon is any closed plane figure whose sides are straight line segments. Examples of polygons include triangles, quadrilaterals (including squares, rectangles, parallelograms, rhombuses, and trapezoids), pentagons, hexagons, and octagons. The sides of a polygon are sometimes called edges, and the corner points are known as vertices. A polygon always has the same number of edges and vertices, and each vertex has a corresponding angle. Together, the edges of a polygon form a closed polygonal curve.

In analytic geometry, a polygon can be specified by the coordinates of its vertices. Each edge of a polygon can be described by a linear equation, making polygons computationally simpler than any other kind of shape. For this reason, polygons are extremely important in computational geometry, and are widely used in computer graphics to represent surfaces in three dimensions. (See the article on polygonal modeling.)