In 3ds Max there are two levels of editing and creation of objects.
Mesh. The TriObject class represent the data that flows through the geometry pipeline.MNMesh. The PolyObject class objects are what actually flow through the geometry pipeline. The EPoly class provides an editable interface to PolyObject.PatchMesh is the primary class for working with patch meshes. Internally a PatchMesh is converted to a Mesh, so a PatchMesh flows down the pipeline as a collection of TriObjects.SplineShape is made up of Spline3d objects. Some modifiers can act on spline shapes.NURBSObject can be one of several kinds of NURBS types such as NURBSPoint, NURBSCurve, and NURBSSurface. Some modifiers can act on generic NURBS objects.Modifier::InputType() method.