it is the square
Rectangles and squares
A quadrilateral. (which may have a pair of parallel sides, or two pair, as follows:) If opposite sides are parallel and equal in length, but angles are not right angles, it is a rhombus. If opposite sides are parallel, all angles are right angles, but there are two sides longer than the other two, it is a rectangle. If all four sides are the same length, and all angles are 90°, it is a square. It is also a Trapezium e.g Rectangle.
A square or rectangle are the only regular polygons, but many other shapes have two right angles and two parallel lines.
a square and a rectangle
There are no parallel sides on a nonagon (nine-sided figure)... Regular shapes with an odd-number of sides have no parallel sides.
Polygon
Any polygon with 2n sides (n integer) where opposite sides are parallel, will have its opposite angles congruent.
If all the sides and all the angles are the same and in the same order, the shapes are congruent.
Some shapes have angles and so they are important in defining the shapes. And angles are absolutely critical for angles. They are the very essence of their existence: if it were not for angles then there would be no angles.
Both shapes have 4 sides, 4 right angles and 2 parallel pairs of lines.
Squares have 4 90 degree angles and 2 sets of parallel lines and 4 congruent sides. A rectangle has the angles and parallel lines. A parallelogram has the parallel lines. A rectangle is most similar, however there are more geometric shapes with some similarities to a square.
A rectilinear figure is a polygon such that all its sides meet at right angles. The only convex shapes are a rectangle (or square), but it can also be a concave shape with some interior angles of 270 degrees.