square, closed plane figure bounded by four straight line segments of equal length and meeting at right angles. The points of intersection of the lines, or sides, are called vertices. The diagonals of a square are the two lines joining opposite vertices; they are of equal length and are the perpendicular bisectors of one another. The perimeter of a square is the sum of the lengths of its sides, or P = 4 s, where s is the length of a side. The area enclosed by a square is A = s 2. The square is one of the commonest geometric figures and has long had various symbolic meanings in religion and art.