rom is a backup copy of a game you can use with your computer. To
get it, you need to plug your computer with your Super Nintendo
(if you want to get a Super Nintendo ROM). Once you have put the
game, with a special software, you can copy the content of the cartridge
to your computer. You got the ROM.
your computer need a software called an emulator. This emulator
will behave like the Super Nintendo and you'll be able to play SNES
games with your computer.