What is a one-sided polygon called?

Hint: In this problem we need to identify the name of the one-sided polygon. For this we will first look at the definition of the polygon and different parts or elements of the polygon. Afterwards we will look at the different types of the polygons with diagrams and their names. After that we will look into the question and identify the answer for the question.

Complete step-by-step solution:
In the problem we can observe that term polygon. The definition of the polygon is listed below.
A two-dimensional geometric shape which has closed structure with finite line segments. The line segments which form the polygon are called as sides or edges and the points where the line segments are connected each other is called as vertex. The line segments or sides of a polygon should be connected to each other in a manner that the formed shape should be closed that means there is no gap or disconnection between the sides.
Some of polygons with their name and shape are listed below

The above closed shape is formed with three sides. So, we can call it as a polygon and the name of the polygon is Triangle.

The above closed shape is formed by joining four-line segments. So, we can call this a polygon and the name of the polygon is quadrilateral.
Now we need to find the name of the polygon with one side. We can draw the one-sided polygon as

We can observe that there is no closed shape formed with one line. So, we cannot form a polygon with one side.
Hence there is no possibility to form a one-sided polygon.

Note: By observing the definition of the polygon we can say that to form a closed shape we need to have at least three sides or three-line segments. So, we cannot form a polygon with one side or even with two sides also.