This document defines and classifies different types of quadrilaterals. It introduces quadrilaterals and defines special types including parallelograms, rectangles, rhombuses, squares, and trapezoids. Quadrilaterals can have multiple names because some properties overlap between types. The best name is the most specific one. The document shows how the types are related through Venn diagrams and concept maps, and provides examples of classifying quadrilaterals and identifying the best name.