trapezoid
A four-sided building plan with nonparallel sides, distinguished here from square and rectangular plans.
A trapezoidal footprint plan is defined as a four-sided plan with two sides which are not parallel. Although linguistic usage allows the term to be applied to any four-sided polygon, the more restrictive usage distinguishes it from other shapes such as squares and rectangles.
The four-sided outline can have unequal side lengths and unequal corner angles. The definition uses the nonparallel sides to distinguish the form from a square or rectangle.
A parallelogram has two parallel pairs of opposite sides and non-right-angle corners. The neighboring definitions describe those more specific arrangements; the trapezoid definition above does not state that an additional pair of sides must be parallel.