Is trapezoid a special parallelogram? Really or not?

The trapezoid is a special parallelogram, which is wrong. A parallelogram has two parallel sides, and a trapezoid has one and only one set of parallel sides. The key is that a trapezoid has only one set of parallel sides. When a trapezoid has two sets of parallel sides, it is not a trapezoid, so a trapezoid is not a special parallelogram.

Parallelogram is a closed figure composed of two groups of parallel lines on the same two-dimensional plane. A parallelogram is a simple (non-self-intersecting) quadrilateral with two pairs of parallel sides.

A trapezoid is a quadrilateral with only a set of parallel opposite sides. Two parallel sides are called the bottom of the trapezoid: the longer bottom is called the lower bottom, and the shorter bottom is called the upper bottom. The other two sides are called waist, and the vertical section sandwiched between the two bottoms is called trapezoidal height.