A Pluggable Database (PDB) is a user-created collection of schemas, objects, and related structures that logically appears to client applications as an independent database.
Regardless of who creates the PDB, it is always owned by the SYS user. SYS is a common user within the Container Database (CDB), meaning it maintains the same identity across the root container and all existing or future PDBs.
PDBs are designed to be plugged into CDBs, allowing for flexible database management. A single CDB can host multiple PDBs, each of which is accessible over the network as a distinct database.