HttpSession interface is defined in "javax.servlet.http" package and is used for the purpose of session tracking while working with servlets. Session tracking is a mechanism that is used to maintain state about a series of requests from the same user (that is, requests originating from the same browser) across some period of time. The session object can be found using getSession() method of the servlet request object. With the help of this interface the servlet can view and manipulate information about a session, for example, session id, creation time, last accessed time and can bind the objects containing user information to the session. Storing all these information to the session persists across series of requests from the same user.
Read more at:
Recommend the tutorial