Free-Form (NURBS) Surfaces
A non-uniform rational B-spline (NURBS) surface is the most mathematically flexible way to represent a surface in a model. A B-spline surface is easy to modify because each pole of its control net affects the shape of the surface only over a limited part. The control net is analogous to a B-spline curve's control polygon.
Tip: Before working with 3D NURBS surfaces, it is a good idea to become familiar with 2D B-spline concepts and placement. For more information, see Using Curves.