A ROM (Read-Only Memory) is a copy of a game's data, often extracted from a game cartridge or disc. In the case of Skyward Sword, a ROM would contain the game's data, including its code, graphics, and soundtracks. WBFS ( Wii Backup File System) is a file system used to store Wii game backups. A WBFS file is essentially a container that holds a game's data, including its ROM.