A session can be defined as a server-side storage of information that is desired to persist throughout the user's interaction with the website or web application.
Instead of storing large and constantly changing information via cookies in the user's browser, only a unique identifier is stored on the client side (called a "session id"). This session id is passed to the web server every time the browser makes an HTTP request (i.e., a page link or AJAX request). The web application pairs this session id with it's internal database and retrieves the stored variables for use by the requested page.
Last Revised: 2015-08-29