In general, a NURBS surface, NURBS curve, subdivision surface, or polygonal surface (mesh).

• Appendix A: NURBS Geometry
• Geometry constraints

Links on converting geometry from one type to another:

• Prepare a polygonal surface for conversion to a subdivision surface
• Prepare a NURBS surface for conversion to a subdivision surface
• Convert a NURBS or polygonal surface to a subdivision surface
• Convert a subdivision surface to polygons
• Convert a subdivision surface to a NURBS surface