The trapezium has just one pair of lines parallel. The parallelogram goes a step further. If both pairs of opposite sides are parallel, the shape is a parallelogram.

The shape enclosed by the four lines in the diagram is a parallelogram, because both pairs of opposite sides are parallel. This mean means that both pairs of opposite sides are equal in length too.

So there are two aspects to any parallelogram.
Opposite sides will be equal in length.
Opposites sides will be parallel.
If one is true the other must be true as well.

With a parallelogram, the opposite corner angles are equal.

A parallelogram which also has all its angles as right angles (90°) is called a rectangle. Remember this definition as well, although we cannot make any rectangles with Isotiles.