“Other” is all storage not otherwise included in the main categories. It may, for example, include miscellaneous files no longer in use, caches, previously streamed videos and music, etc. And occasionally a corrupted file that can't be deleted.
Restoring is the next troubleshooting step available to you. First, try restoring from a backup, because most ”other” files are not part of backups. If still no success, you likely have a corrupted file and will need to restore as new.
Restore instructions: https://support.apple.com/en-us/HT204184
About storage on your device and in iCloud: https://support.apple.com/en-us/HT206504