MAME 0.250 is a specific release of the Multiple Arcade Machine Emulator. A “ROM set” for MAME means a collection of game ROM images (and supporting files) matched to that MAME version. Using the correct ROM set ensures games run without missing files or compatibility errors.
Because MAME is constantly improving its accuracy, the way it reads these files changes. A ROM that worked in version 0.150 might be named differently or require a different "BIOS" file in version 0.250. This is why casual collectors often stick to specific, stable versions of the emulator and match them with a corresponding "Full ROM Set." mame 0250 rom set