A trapezium is a quadrilateral with only one pair of parallel lines but a parallelogram has two pairs of parallel lines. So, parallelogram is a special type of a a trapezium.
a parallelogram is afour sided plane rectilinear figure with opposite sides parallel whereas a trapezium is a quadrelateral with one pair of sides parallel. That is why a parallelogeam can be thought of as a special trapezium.