The DOMAIN user is a special
database user of the database user class DBA. The DOMAIN user is the owner of the system tables of the database catalog.Just like the
SYSDBA user, the DOMAIN user is created when a database instance is installed. The DOMAIN user is created by the system under the pre-defined name DOMAIN. The password is the same as that of the SYSDBA user that was created earlier.The DOMAIN user’s password can be changed at a later date.