A rectangle
is a quadrilateral all of whose angles are right angles, like a
page of this book or the shape of most windows and doors.

In a rectangle,
opposite sides are parallel and equal in length; diagonals are equal
in length and cut each other in half. Except when it is a square
it has two lines of symmetry and rotational symmetry of order two.
An oblong is a rectangle which is not a square.

A special quadrilateral, a parallelogram with interior angles of
90. Its opposite sides are equal in length and parallel. It has
two lines of symmetry, and its rotational symmetry is of order two.