Like the Shape object, a NURBS model can be an assemblage of multiple NURBS sub-objects. For example, a NURBS object might contain two surfaces that are separate in space. You control NURBS curves and NURBS surfaces with point or control vertex (CV) sub-objects. Points and CVs behave somewhat like the vertices of spline objects, but there are differences.
The parent object in a NURBS model is either a NURBS surface or a NURBS curve. Sub-objects can be any of the objects listed here. A NURBS curve remains a Shape object unless you add a surface sub-object to it when you convert it to a NURBS surface (without changing its name).
There are two kinds of NURBS surfaces. A point surface is controlled by points, which always lie on the surface. A CV surface is controlled by control vertices (CVs). Instead of lying on the surface, CVs form a control lattice that surrounds the surface. (This is similar to the lattice used by the FFD [free-form deformation] modifiers.)
See Creating Surface Sub-Objects and Editing Surface Sub-Objects.
There are also two kinds of NURBS curves. These correspond exactly to the two kinds of surfaces. A point curve is controlled by points, which always lie on the curve. A CV curve is controlled by CVs, which don't necessarily lie on the curve.
See Creating Curve Sub-Objects and Editing Curve Sub-Objects.
Point surfaces and point curves have point sub-objects. You can also create separate point sub-objects that are not part of a surface or a curve.
CV surfaces and CV curves have CV sub-objects. Unlike points, CVs are always part of a surface or a curve.
See Editing Curve CV Sub-Objects and Editing Surface CV Sub-Objects.
Imports are 3ds Max objects, including other NURBS objects. Within the NURBS model, they render as NURBS; but they retain their original parameters and modifiers.
See Attaching and Importing 3ds Max Objects.
Sub-objects can be dependent sub-objects whose geometry is related to the geometry of other sub-objects.