Single user mode

Roughly analogous to "repair/install mode". Depending on your configuration (which runlevel you're on, which security measures you've run and what you're booting off of,) you're given the prompt for the root password and then offered the chance to fix or install whatever you need.

The second CD in the FreeBSD set is a FixIt disk that boots you into single-user mode.

See also init and the man page for init.