The "rar" extension indicates a compressed WinRAR file. If you found this string on a forum or imageboard, it is likely a unique filename or a password for a specific download.
Based on the format, here are the most likely possibilities: GDBXIJJG rar
The sequence "GDBXIJJG" could be a simple substitution cipher (like ROT13 or a Vigenère key) or a specific hash used to identify a file on peer-to-peer networks or "deep web" archives. The "rar" extension indicates a compressed WinRAR file