A quadrilateral with exactly one pair of opposite parallel sides is called a trapezoid. As with all quadrilaterals, the sum of the interior angles of a trapezoid is always equal to 360 degrees.
All trapezoids have at least one acute and one obtuse interior angle, although they most frequently have two of each, with the obtuse angles adjoining the shorter parallel side and the acute angles adjoining the longer. However, it is possible for a trapezoid to have exactly two right angles if they adjoin the same non-parallel side. If a four-sided figure has four right angles, it is a rectangle, not a trapezoid.