Client-server systems are defined by servers providing information services to clients. Usually, there are more clients than servers, so servers need a way to keep track of which client is which. A "session" is a single client's conversation (usually involving many request/response roundtrips) with a logical server (which may be formed of one or more physical servers). Session state is client-specific data that is accumulated during the session.
J2EE Platform Overview
HttpSessionbe used to track session state.