MVS - Mitral Valve Stenosis, or a thickening of the mitral valve.
MR - Mitral regurgitation, or a leaky mitral valve
It's good that you don't have either of those.
Thin and mobile probably means there is no thickening, and it's moving and working as it should. You can always call your doctor to help you understand your results. Do you have a follow up appt scheduled to go over your results?