it is any shape with 4 sides
A plane shape with four vertices (corners). Usually the same as a quadrilateral, but can also include the shape formed by an X with two sets of opposite ends joined together.
It is a typographic oxymoron.There is no such thing as a quadrangel: the nearest real word is quadrangle and that is a 2-dimensional shape with four sides. It cannot, therefore, be a shape with six sides!