Session is a way through which a series of tasks can be performed in a systematic order without mislaying previous traces. session is meant to surmount the drawback "stateless server".
Protocol like HTTP is a "stateless" protocol which means not having any information about previous task [i.e.each request for a new page is processed without any knowledge of previous pages requested.]. Hence, Session solves this problem by creating unique identity of each user using the application. It allows to store user information on the server for later use. Site Administrator maintains the default time frame of the user session [e.g. 30 min] if the user revisit the site within that time span it will considered one user session because any number visit within that time frame will only count as one session. If the visitor returns to the site after the expiring of allotted time frame the session expires.
