A jailed shell is a kind of limited shell that provides the user with a very real looking shell but does not allow him to mess with/view/modify any parts of the real file systems. The file system inside the shell is different from the actual file system of the underlying system. Such a functionality is achived through chroot and finds many kinds of applications. For example to setup a linux shell for users to just “play with”. Or run some program with full functionality but in a limited environment and so on.