A polygon with five sides is known as a

A polygon with five sides is known as a pentagon.

Explanation:

A polygon is a closed figure made up of straight line segments.
The number of sides a polygon has determines its name.
For a polygon with 5 sides, the prefix "penta-" refers to five, and "-gon" refers to a shape with sides. Therefore, a polygon with five sides is called a pentagon.
Key properties of a pentagon:

It has 5 sides.
It has 5 vertices (corners).
The interior angles of a regular pentagon (where all sides and angles are equal) sum to 540 degrees.
In summary, a polygon with five sides is called a pentagon.