Polygons are closed plane shapes with straight sides, such as squares, triangles, and shapes with more sides like pentagons and hexagons. Polygons are distinguished by the number of sides they have, with triangles having 3 sides and angles, quadrilaterals having 4 sides and angles, and so on. Polygons can be either regular, meaning all sides and angles are equal, or irregular, where sides and angles are not equal.