This filename represents the second part of a split compressed archive for the game (POKUM) for the Nintendo 3DS. POKUM : An acronym for Pokémon Ultra Moon . EUR : Specifies the European region release of the game.
: Signifies the game includes eight language options (likely English, French, Italian, German, Spanish, Japanese, Korean, and Chinese).
: Likely stands for Decrypted , meaning the file has been processed so it can be played on emulators like Citra or on a hacked 3DS without needing original console keys.