Which of the following best describes a side of a polygon?

A side of a polygon is defined as a straight line segment that connects two vertices. In the context of geometry, polygons are made up of multiple sides that enclose a space. Each side represents one of the straight edges of the polygon, linking two corner points or vertices. This characteristic is fundamental in distinguishing polygons from other shapes, as every side must be a linear segment connecting these points.

The other descriptions provided do not accurately represent the concept of a side. A curved line segment cannot be a side of a polygon, as polygons consist solely of straight lines. A vertex is not a side but rather a point where two sides meet. Furthermore, a point in the interior of a polygon does not describe a side either since it's located inside the shape rather than forming part of its boundary. Thus, the definition of a side as a straight line segment connecting two vertices is essential in understanding the structure of polygons.