|A NURBS surface is like a rectangular stretchy rubber sheet. The NURBS form can represent simple shapes, such as planes and cylinders, as well as free-form, sculptured surfaces. All NURBS surfaces have an inherently rectangular organization.|
|Part of||Rhinoceros , Rhinoceros for OSX|
Non-Uniform Rational B-Splines, are mathematical representations of 3-D geometry that can accurately describe any shape from a simple 2-D line, circle, arc, or curve to the most complex 3-D organic free-form surface or solid.
See this overview of NURBS geometry for more information.