from
The Free On-line Dictionary of Computing (8 July 2008)
chroot
<operating system> The {UNIX} command to make the {root
directory} (/) become something other than its default for the
lifetime of the current process. It can only be run by
privileged users and is used to give a process (commonly a
network server such as {FTP} or {HTTP}) access to a restricted
portion of the {file system}.
The new root contains copies of all the essential files and
directories, e.g. /lib, /dev/tty, /tmp.
(1996-12-08)