In the strictest technical sense, a ROM (Read-Only Memory) is the data chip inside an arcade cartridge or cabinet that contains the game code. A "ROM file" is a digital copy of that chip.

A ROM (Read-Only Memory) is a file that contains the data from a classic arcade game. In the context of MAME4droid, a ROM is the game data that is required to play a specific arcade game.

You are not alone. MAME is not like a console emulator (SNES, Genesis, etc.). With MAME, the version of the emulator must match the version of the ROM set. Here is everything you need to know.

When you download a ROM for MAME, you are essentially downloading a zip file containing the binary code of a game like Pac-Man or Street Fighter II . MAME4droid reads this code and simulates (emulates) the original hardware that would have run it.

There are currently three main versions of this emulator available on the Google Play Store, each requiring a specific romset:

Because of copyright laws, the emulator does not come with games. You must source your own "zipped" ROM files from reputable preservation sites: Which mame4droid i should use? : r/EmulationOnAndroid