The meaning of this parameter differs according to the database engine you use. For example, this value returns MySQL, MariaDB, or PostgreSQL information when returning values from CreateDBInstanceReadReplica since Read Replicas are only supported for these engines.
MySQL, MariaDB, SQL Server, PostgreSQL, Amazon Aurora
Contains the name of the initial database of this instance that was provided at create time, if one was specified when the DB instance was created. This same name is returned for the life of the DB instance.
Contains the Oracle System ID (SID) of the created DB instance. Not shown when the returned parameters do not apply to an Oracle DB instance.