A 4-sided flat shape with straight sides that has a pair of opposite sides parallel.

The sides that are parallel are called "bases". The other sides are "legs" (which may or may not be parallel).

*(Called a trapezium in the UK. Both US and UK definitions of trapezium and trapezoid are swapped over.)*The sides that are parallel are called "bases". The other sides are "legs" (which may or may not be parallel).

See: Trapezium