A rootshell is a UNIX-shell on which the 'root' user of a UNIX-system operates. This shell is granted all privileges and the abilities to modify and delete all files on such a system. A rootshell differs from a regular shell (e.g a shell on which a normal user operates), which may not have these privileges granted.

A rootshell usually looks something like

root@host#

in plain. This however, is all relative.