-r means delete recursively. rm will by default only remove files, but with this flag, it’ll also delete all the folders, subfolders, and the files in those.

--no-preserve-root disables a security check. A few years ago, this flag didn’t exist. If you ran rm -r /, everything on your system would be deleted, provided the user had permissions. Now, / is treated specially and rm will refuse to perform a recursive delete on it without the --no-preserve-root flag.

-f means force and disables any prompts.

rm -rf --no-preserve-root / would delete every file on your system.