The file has been "decrypted," meaning the Nintendo 3DS encryption has been removed. This allows the game to be played on PC or Android emulators like Citra , rather than requiring a modified ("hacked") physical 3DS console.
A .rar file is a compressed archive containing the .3ds or .cia game file. EOU-TMG-(UNDUB)-DecrTD-Ziperto.rar
If you're asking about this for technical or archival reasons, I can also explain: How to What the differences are between this and the original Where to find other similar modified ROMs The file has been "decrypted," meaning the Nintendo
This refers to the source website that provides these modified ROMs, which frequently hosts decrypted and undubbed versions of Atlus games. The file has been "decrypted