ROM

A ROM (Read-Only Memory image) is a binary copy of the contents of a game cartridge or disc. The name dates to the era when game data lived on actual ROM chips inside cartridges. A ROM file holds the same bytes the original chip held, byte-for-byte; an emulator loads it and reads from it the same way the original console did. ROMs are typically copyrighted; legal status depends on whether you dumped it from hardware you own.