What role does the Session interface play in Hibernate?

The Session interface is the primary interface used by Hibernate applications. It is a single-threaded, short-lived object representing a conversation between the application and the persistent store. 
Session session = sessionFactory.openSession(); 
Session interface role:

• Wraps a JDBC connection
• Factory for Transaction
• Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier