Multitenancy is a new concept in Oracle 12c. The basis of it is that, you can separate the application data from the system data. Up to and including 11g, all the data in the database was residing in the same dimension as the system data or any other data for that matter. Data related to different application, were in the same tablespaces or even managed by the same user. Well, from 12c, all this can go under the table, now you can have many databases PDBs (pluggable databases), inside one big database, the root container. There are even more possibilities like application containers and so on, but we will see that later.

With the multi-tenancy, we have a:

• root container - Where the system data resides. Also you can choose if you want the UNDO tablespace in the root to be used for all PDBs, or each PDB to have its own undo, SYSTEM and SYSAUX tablespace, making it completely independent from the root container.