A regular polygon is a two-dimensional shape with all sides and angles equal. Common examples include the equilateral triangle, square, and regular hexagon. The number of sides determines the name of the polygon, such as a pentagon for five sides or an octagon for eight sides. Regular polygons can be classified based on the number of sides they have. They are often studied in geometry for their symmetry and properties. The interior angles of a regular polygon can be calculated using the formula (n-2) \times 180/n, where n is the number of sides.