A standby database is a copy of the active database instance.
You update a standby instance at regular time intervals using log backups from the original instance. The standby instance is always in operational state ADMIN.
If the original instance fails, you can activate the standby instance immediately, thereby continuing work without long downtimes. Depending on the configuration that is selected, you can start the standby instance in a status that corresponds to the status of the original instance at a point in time in the past.
Original instance and standby instance
Activating the Standby Instance