A trapezoid is a four-sided figure, with only one pair of parallel sides.  There can be no more than two right angles (lest it be a rectangle), or there could be no right angles.  If there is only one right angle, it can only be a quadrilateral.  On each of the non-parallel lines, the sum of the angles created is equal to 180 degrees, always.  If the two angles created by one of the parallel lines are equal to each other, the angles created by the opposite line must also be equal to each other and the trapezoid will be symmetrical and isosceles.  If the angles opposite each other are equal to each other, than it is a parallelogram and not a trapezoid.