Trapezium (Polygon video #4)
Disclaimer
In my country, (and in a lot of countries)
Trapezium is a quadrilateral with (at least) one pair of parallel sides.
Trapezoid is a quadrilateral with NO parallel sides.
In the US, the definitions are commonly flipped. So if you are in the US, you may need to modify the lesson.
Also, the video uses the 'inclusive' trapezium definition where rectangle and square (as well as parallelogram) are considered special cases of trapezium. Some country may use the 'exclusive' definition: Trapezium is a quadrilateral with ONLY one pair of parallel sides.
Tough, isn't it?