A regular quadrilateral is a square, as it is the only quadrilateral with four equal sides and four equal angles. A square has four lines of symmetry: two lines through the midpoints of opposite sides (horizontal and vertical) and two lines along the diagonals. It also has rotational symmetry of order 4, meaning it maps onto itself when rotated by 90°, 180°, 270°, and 360°

. In summary, a regular quadrilateral (square) has:

• Four lines of symmetry
• Rotational symmetry of order 4

No other quadrilateral has the combination of equal sides, equal angles, and this high degree of symmetry.