An edge.
a line
To answer this question more details need to be provided. For example one a 3D shape one side is called a face.
no shape
The faces in a 3-D shape (polyhedron, for example) are bordered by edges.
Any one of the plain surfaces of a solid, three-dimensional shape. Also Called -- side
One side of a face in a 3D shape refers to a flat surface that forms part of the outer boundary of a three-dimensional object. In geometric terms, this is often called a "face," which can be a polygon like a triangle or rectangle. For example, in a cube, each side of the cube is a face, and there are six such faces in total. Each face contributes to the overall shape and volume of the 3D object.
A sphere
A blob.
A Moebus strip.
It is a face.
Circle. Sphere.
The side of your face is called the profile