Linux.com: Unix Web Application Architectures – Part 3: Sessions, Authentication, and Databases

“With a session I mean the series of HTTP requests/replies that
one user makes when visiting a site. In the example application, a
session would begin when a customer logs on in the system, and end
when the customer logs off or just closes his browser.”

“Session state is all relevant information about what the user
has already done during that session. In our example application,
the following session state data might be kept….”

Session management is a significant and very fundamental
issue with web applications, because HTTP is a completely stateless
Each HTTP request has no relation with any other
HTTP request (aside from possibly using the same TCP connection).
Therefore, it’s the job of the application to create this
association. In traditional GUI programming, each screen element is
represented by a GUI toolkit object that holds all the data and
state of the screen element. In web applications, this data must be
kept somewhere else.”