High Quality Content by WIKIPEDIA articles! In computer science, a session identifier, session ID or session token is a piece of data that is used in network communications (often over HTTP) to identify a session, a series of related message exchanges. Session identifiers become necessary in cases where the communications infrastructure uses a stateless protocol such as HTTP. For example, a buyer who visits a seller`s site wants to collect a number of articles in a virtual shopping cart and then finalize the shopping by going to the site`s checkout page. This typically involves an ongoing communication where several webpages are requested by the client and sent back to them by the server. In such a situation, it is vital to keep track of the current state of the shopper`s cart, and a session ID is one way to achieve that goal.