A quadrilateral is a four-sided figure. Several types of quadrilaterals have special names:

A square is a quadrilateral with four equal sides and four equal (right) angles. | |

A rectangle is a quadrilateral with four equal (right) angles. | |

A rhombus is a quadrilateral with four equal sides. | |

A parallelogram is a quadrilateral with two pairs of parallel sides. | |

A trapezoid or a trapezium is a quadrilateral with one pair of parallel sides. | |

There are other quadrilaterals for which none of the above definitions apply. |

It can be seen from the definitions that all squares are rectangles and rhombuses, and all rhombuses and rectangles are parallelograms. The reverse is not necessarily true, however.