What is a polygon?

A polygon is defined as a closed figure that consists of three or more straight sides. This definition captures the fundamental characteristics of polygons, which include having a defined number of edges (sides) and vertices (corners), with each side being a straight line segment. Polygons can vary in the number of sides they have, leading to classifications such as triangles (three sides), quadrilaterals (four sides), pentagons (five sides), and so forth.

The other options do not accurately reflect this definition. A shape with only three sides describes a specific type of polygon (a triangle) but does not encompass the broader definition applicable to all polygons. Similarly, a closed figure with two straight sides fails to meet the requirements for a polygon since a minimum of three sides is necessary to enclose a space. Lastly, figures that can have curves are not polygons, as this characteristic contradicts the polygon's requirement for straight sides. Thus, the correct choice encompasses the essential attributes of polygons comprehensively.