Which of the following best defines a polygon?

A polygon is best defined as a closed figure with straight sides. This definition captures the essential characteristics of polygons: they are formed by connecting a finite number of line segments, which are known as sides. Each segment meets exactly two others at points called vertices, creating a complete shape.

Polygons can have various numbers of sides, ranging from a triangle (three sides) to a quadrilateral (four sides) and beyond. The important elements of being a polygon include having straight sides (as opposed to curved or rounded edges) and being a closed figure, meaning there are no open ends or gaps in the shape.

This definition excludes figures that are not polygons, such as those with curved sides or no sides at all. Thus, "A closed figure with straight sides" is the most accurate characterization of a polygon.