The multitenant architecture introduces the concepts of CDB (Container Database) and PDB (Pluggable Database).
CDB - Multitenancy allows users to have multiple virtual databases called containers. These containers exist inside one physical database called a container database (CDB).
PDB - The containers are easily plugged into or unplugged from the container database. Thus these containers are also known as pluggable databases (PDBs). The pluggable databases behave just like normal databases.