Which quadrilateral is defined as having at least one pair of parallel sides?

Order from most general to most special:

```
Quadrilateral
├── Trapezium (one pair of parallel sides)
├── Kite (two pairs of adjacent equal sides)
└── Parallelogram (two pairs of parallel sides)
├── Rectangle (4 right angles)
│ └── Square (4 right angles + all sides equal)
└── Rhombus (4 equal sides)
└── Square (also)
```

A square is BOTH a rectangle and a rhombus — it's the most special kind of parallelogram. A rectangle and a rhombus are both parallelograms. Trapeziums and kites are quadrilaterals but not parallelograms.