Definition( Extended-MHD ):

Any plasma model which supports MHD waves in a fluid or a partially fluid picture.

Rationale of the definition:

The MHD model is well established in theory and practice.
The Extended-MHD concept connects between MHD model and a comprehensive model
which can include all the relevant physics such as gyroviscosity, anisotropic pressure,
wave-particle resonance and trapping, electron inertia, etc.

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