What do you call a plane figure with four sides?

A plane figure with four sides is known as a quadrilateral. The term "quadrilateral" is derived from the Latin words "quadri-" meaning four and "latus," meaning side. This classification includes various shapes such as squares, rectangles, trapezoids, and parallelograms, all of which have four sides.

In contrast, a triangle is defined as a polygon with three sides, while a hexagon has six sides. A circle, on the other hand, is not a polygon; it is a round shape that is defined by a continuous curve with all points equidistant from a center point. Understanding these definitions is essential in geometry, where identifying and classifying shapes based on the number of sides is fundamental.