Looks like you can do lots of fun stuff here in case you get a stalled system.
Quite fun that this is a quite useful thing and I have never heard of this before. Maybe Linux community is being quiet about this because it’s close to ctrl-alt-del :)
mnemonic: BRUISER (REISUB)
unRaw (take control of keyboard back from X), tErminate (send SIGTERM to all processes, allowing them to terminate gracefully), kIll (send SIGKILL to all processes, forcing them to terminate immediately), Sync (flush data to disk), Unmount (remount all filesystems read-only), reBoot.