In organization you may use personal tags. These tags are associated with the records. Now deactivate one of these users. When you deactivate a user those tags still remain in the records. To remove these tags we have Personal Tag Cleanup. Only deactivated user’s tags will be displayed in the list.
Setup > Customize > Tags > Personal Tag Cleanup
Personal Tag Cleanup > Select Users and Delete. Tags associated with this user will be deleted from the records.