Don't remember the exact acronym, but it's basically an emulator (the E of MAME) for the programs (ROMS) that used to run in the early video games. The ROMS are/were read only chips used to hold the programs in these old machines. The programs were extracted and can be run inside the emulator (a piece of software running on your PC/Mac/Linux box). So you basically get to play your old arcade favorites (the REAL THING) on your PC. Of course building a cabinet to hold your PC so you get the 'feel' is just so much cooler...not that I have, but now that I think about it...

-Zeke