The Maya API uses a convention of prefixes on its classes to distinguish the various types of C++ objects that it uses.
Any class with this prefix is a function set used to operate on MObjects of a particular type.
These classes are iterators and work on MObjects much the way a function set does. For example, MItCurveCV is used to operate on an individual NURBS curve CV (there is no MFnNurbsCurveCV), or iteratively, on all the CVs of a curve.
Classes with this prefix are all Proxies, API classes designed for you to derive from and create your own object types.
Most of these classes are Wrappers, though there are others. For example, Function sets is a handle on Maya’s internal objects, and MGlobal is a class of static methods that operate globally and do not require an MObject on which to operate. (See Selecting with the API for information on MGlobal.)
