DB_UNIQUE_NAME and DB_NAME parameter in Oracle
DB_UNIQUE_NAME: specifies a name that uniquely identifies the databases in the Data Guard configuration. It is used in while creating Data Guard which specified remote location.Databases with the same DB_NAME within the same DB_DOMAIN must have a unique DB_UNIQUE_NAME. It is used in LOG_ARCHIVE_CONFIG parameter values for remote location.Log transport services validates that the db_unique_name of the database that specified destination.
DB_NAME: It is the identifier of exact database. It should be the same in both the standby and production initialization parameter files
Note: DB_NAME for all standby databases must match the DB_NAME of the primary database.