The lightwave version of NURBS (Non-Unirform Rational B-Splines.) In Lightwave version 6 and beyond it is referred to as subpatches. Used to take regular 3 or 4 sided polygons and turns their edges into splines. That is, a more detailed curved surface modeled by mathematic formulas. From there the subpatched surfaces can be transformed in a more believable organic form.
For less computer intensive work or rendering the nurbs are frozen into polygons that approximate the curved surfaces. The advantages provided by metanurbs or subpatches are that models are much softer and curved, and a great deal of believability can be lent to objects that are normally very organic.