The below content is based on a David Peake‘s presentation at OOW 2012 and APEX World 2013.
As the Oracle Database 12c is not out yet at the time of writing, note that things might be different in the final product.
The Oracle Database 12c is a major release in Oracle history, as it contains a complete redesign of the underlying architecture. Two things will come back a lot when you read about Oracle DB 12c; the Container Database (CDB) and the Pluggable Database (PDB).
The below image shows how it works; you have a container database which the memory and processes are attached at, and then you can have multiple other databases that you can just plugin.
You find more information about this architecture here.
So what does Oracle DB 12c mean for APEX? Find out on my blog post.