Edition-Based Redefinition 18c

Edition-based redefinition (EBR) enables online application upgrade with uninterrupted availability of the application. When the installation of an upgrade is complete, the pre-upgrade application and the post-upgrade application can be used at the same time. Therefore, an existing session can continue to use the pre-upgrade application until its user decides to end it; and all new sessions can use the post-upgrade application. When there are no longer any sessions using the pre-upgrade application, it can be retired. In this way, EBR allows hot rollover from from the pre-upgrade version to the post-upgrade version, with zero downtime.

https://docs.oracle.com/en/database/oracle/oracle-database/12.2/adfns/editions.html#GUID-C213A6AA-5427-4426-80B5-D5301386253E

https://www.oracle.com/database/technologies/high-availability/ebr.html