Safe-rm is a safety tool intended to prevent the accidental deletion of important files by replacing /bin/rm with a wrapper, which checks the given arguments against a configurable blacklist of files and directories that should never be removed.
Users who attempt to delete one of these protected files or directories will not be able to do so and will be shown a warning message instead:
$ rm -rf /usr
(Protected paths can be set both at the site and user levels.)
Source: Safe-rm in Launchpad