It is a face.
Any one of the plain surfaces of a solid, three-dimensional shape. Also Called -- side
Cone
An orb - Globe - ball
Square
sphere
A two-dimensional shape with one curved side and four straight sides can be created, but there is not specific name for such a shape.
The 2-dimensional shape with one more vertex / side is a decagon.
A three-dimensional shape with one side is known as a "Möbius strip." Although it is not a conventional solid, it can be visualized as a surface with only one continuous side and one edge. When constructed, if you travel along the surface of the strip, you will return to your starting point without crossing an edge, demonstrating its unique property. This fascinating shape is often used in mathematics and art to illustrate concepts of non-orientability.
That is a two dimensional view of a three dimensional object, seen from one side at a time as if you are looking perpendicularly to is. Depth is not shown
A pyramid.
Denaturing!
One possible answer is a 2-dimensional shape with a curved side.