Perimeter of a closed figure is the distance covered in one round along the boundary of the figure.  A closed figure in which all sides and angles are equal is called a regular polygon.  Perimeter of a rectangle = 2 × (length + breadth) Perimeter of a square = 4 × length of its side Perimeter of an equilateral triangle = 3 × length of a side The amount of region enclosed by a plane closed figure is called its area. Area of a rectangle = length × breadth Area of a square = side × side