What defines a quadrilateral?

A quadrilateral is defined as a polygon that has four sides. This characteristic makes it distinct from other types of polygons. For example, a triangle, which has three sides, and a pentagon, which has five sides, cannot be classified as quadrilaterals. Similarly, a hexagon has six sides, further differentiating it from the definition of a quadrilateral. The essential feature of having exactly four sides allows for various interesting properties and classifications within quadrilaterals, such as squares, rectangles, trapezoids, and parallelograms, each having unique attributes based on their side lengths and angles.