In a multitenant container database (CDB), a container represents a collection of schemas, objects, and associated structures. Each container within a CDB is uniquely identified by an ID and a name.
A CDB can include zero, one, or multiple user-created pluggable databases (PDBs) and application containers. A PDB is a self-contained, portable set of schemas, schema objects, and non-schema objects that appears to Oracle Net clients as an independent database.
An application container is an optional component created by users within a CDB. It holds both data and metadata for one or more application back ends. A CDB may contain zero or more application containers.