MAME stands for Multiple Arcade Machine Emulator and when used in conjunction with an arcade game's data file (ROMs), MAME Plus! will more or less faithfully reproduce that game on a PC. MAME Plus! can emulate thousands of classic arcade video games from the 70s, 80s and 90s, and even some from the current decade.
The ROM images that MAME utilizes are "dumped" from arcade games' original circuit-board ROM chips. MAME becomes the "hardware" for the games, taking the place of their original CPUs and support chips. Therefore, these games are NOT simulations, but the actual, original games that appeared in arcades.
As gaming technology continues to rush forward, MAME prevents important "vintage" games from being lost and forgotten. It's incredibly effective once you've loaded a ROM file although for newbies, the process may prove a little but tricky as the interface appears more complicated than it needs to be.