MVS stands for multi video system. NeoGeo had a 1, 2, 4, and 6 slot MVS system. Meaning it can handle 1, 2, 4, or 6 carts. The games cam on carts, like a home console system did.
The MVS system is JAMMA compatible, to a point, the 4th button for each player is in one of the expansion pins on the JAMMA connector.
Note, these things go for some big bucks some times, especially the 4slot system. They are a big collectors item. And they are still being used today. I heard the new Metal Slug 5 is pretty decent.