What is a closed plane figure that is bounded by straight lines called?

A closed plane figure that is bounded by straight lines is termed a polygon. Polygons are characterized by having straight edges and can take various forms, such as triangles, quadrilaterals, pentagons, and so on, based on the number of sides they have.

To understand why this answer is appropriate, it’s important to note that polygons must have at least three sides to be classified as a polygon. The boundaries are made up entirely of line segments that connect at vertices.

In contrast, while a curve can also form a closed figure, it is not limited to straight lines and thus does not fit the criteria specified in the question. A circle, though a closed figure, is defined by a continuous curve rather than straight lines. Lastly, the term solid refers to three-dimensional figures, which are not applicable in the context of a closed plane figure. Therefore, polygon is the correct term to describe a closed plane figure bounded by straight lines.