(John of the clue crew reporting)  Because the geometric shape here has all right angles, it's called a rectangle; when they're not right angles, it becomes this type of quadrilateral
[DOC] [TLE] Full text of "Discovering geometry : an investigative approach" [PAR] Investigation: Defining Angles 1.4 Polygons Investigation: Special Polygons 1.5 
.... Other Shapes 8.5 Areas