parallelogram
A floor plan with 4 sides in 2 parallel pairs which do not meet in right angles.
A building's perimeter is a parallelogram when it has four roughly straight sides, each of which is parallel to its opposite, but which do not meet at 90 degree angles. Two angles must be obtuse and two must be acute. A parallelogram can have four even sides, or two sides which are longer than the other two. It is often referred to as a "diamond" shape.
The opposite sides form two parallel pairs, and the corners alternate between acute and obtuse angles. All four sides can be equal, but equal side lengths are not required.
Square and rectangular plans have right-angle corners and are defined separately here. A diamond-like appearance can describe the orientation of the outline without changing the parallel-side requirement.