What is a one-sided polygon called?
There is no closed shape with one side.
A one-sided polygon is not possible.
There is no polygon with one side, because the definition of a polygon is "a 2-dimensional closed shape".
The minimum number of sides which can close the figure is 3..
One side: a line which is one dimensional
A circle can also does not be considered as a one-sided polygon, because it does not consist of line segments.