What is Session Hijacking?

Web Sessions are usually managed by a "Session Token". Session hijacking is a way of exploiting the web session control mechanism.It's a way to get an unauthorized access to the web-server by stealing a valid token.

Session Hijacking is a type of attack and it can use accomplished by using various techniques like Session Sniffing, Clint Side Attacks like XSS, Man in the middle/browser type of attacks.