A regular polygon is a two-dimensional closed shape in which all the sides are of equal length and all the interior angles are equal in measure. This means the shape is both equilateral (equal sides) and equiangular (equal angles). Examples of regular polygons include the equilateral triangle, where all three sides and angles are equal, and the square, which has four equal sides and four right angles. Regular polygons are symmetrical and have a balanced, uniform appearance.