A mobius loop which has one side and just one edge, could be your answer.
Otherwise, a straight line segment may be it?
A sphere
A vertical line
a quadrilateral
The object you are describing is a circle. A circle has one continuous side with no corners, and its shape is defined by a curved line that is equidistant from a central point. It can also be referred to as a two-dimensional geometric figure.
Spherical
A sphere
A vertical line
a quadrilateral
A line. Or a circle
A cylinder.
Irregular shape is the term given to an object which has 1 flat side, 1 curved side, no corners but has curved edges.
Any curved shape such as a circle, an ellipse, an oval, a wriggly line - as long as it does not have any corners.
The object you are describing is a circle. A circle has one continuous side with no corners, and its shape is defined by a curved line that is equidistant from a central point. It can also be referred to as a two-dimensional geometric figure.
Spherical
a circle
sphere
according to me its octagon