Can you say something about the difference you experience between "plasma fluid dynamics" and "magnetohydrodynamics"?

As I understand it, processes you can treat as MHD practically never occur in nature, and are always something that has been carefully arranged by design so the system can be modeled at all. Astrophysicists seem to treat the two terms as interchangeable. Would you say that MHD suffices to model ion propulsion systems? To model anything, anywhere in nature?