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
A sphere
A blob.
A Moebus strip.
It is a face.
Circle. Sphere.
The side of your face is called the profile
Mobius strip