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.
Denaturing!
A pyramid.
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
One possible answer is a 2-dimensional shape with a curved side.
A rectangular-based pyramid.