Safety island
Beginner
A small, extra-reliable helper inside a big chip. It watches the rest and steps in if something goes wrong.
Novice
A small, separately protected part of a large chip, often lockstep processors plus watchdogs, that monitors the big compute blocks and takes the system to a safe state if they fail.
Expert
Provides watchdogs, fault collection, diagnostics and safe-state control, independent of the monitored domain (separate clock and power where possible).
Explained in Automotive (Industries).