Regionfree Neo Geo

OK, probably a dumbass question but I have to ask anyway.
Is the Neo Geo cartridge system region free by default? Can you
play american and japanese games on a European system?
Or do you have to put some sorta BIOS thingy that you write alot
about here in them to do this?
I have the same question for the Neo Geo CD system? Will I be able to play jap games on my Euro version?

And finally my most embarassing newbie question is, what does
MVS and AES stand for?

AES systems (home neo geo) are region free, but game options will change : no blood and english language on european an us systems, blood and japanese language on japanese system.

AES is Advanced Entertainment System, the hjome version.
MVS is Multi Video System, the arcade version.
MVS cartridges won't fit in AES and vice versa.

Notice that the language of the game you play doesn't depend on what region is the game from, but the region of your system. For example a Japanese game will play in English in an English system. If you mod a NGCD, or change the bios in an AES or MVS system, then you can select the language.

Thanks for explaining. I feel my n00bnes slowly going away!