The storage space taken up by "Other" can be made up of, notes or files of any kind you've added to the iPod whilst using it as a hard disk or album artwork.
There will always be a few MBs of used space under "other" but if it's in GBs it's unusually large.
If the iPod is enabled for disk use, you can look at the folders on the iPod through Explorer or Finder and delete anything you don't want.
Otherwise, see
how to restore the iPod to factory settings which will erase the iPods contents and reclaim the used space.
Then reload the music from iTunes.