quadrilateral: a four-sided figure.
rectangle: a plane figure with four straight sides and four right angles, especially one with unequal adjacent sides, in contrast to a square.
parallelogram: a four-sided plane rectilinear figure with opposite sides parallel.
isosceles trapezoid: a convex quadrilateral with a line of symmetry bisecting one pair of opposite sides.
Just by reading the definitions, I would say this polygon is a parallelogram.