What is a curved surface and a curved edge in geometry 5th grade level?

A curved surface is like imagining a sheet of paper that is bent or a flag waving in the wind. A curved edge is like an elastic stick bent in one(C curve) or more points(S curve).

The curved surface beeing 3 dimensional(3D) and the curved edge 2 dimensional(2D) unlike the simple surface and edge which are 2D respectively 1D.