Safety mechanism
Beginner
A built-in checker that notices when something has gone wrong and reacts.
Novice
A piece of hardware or software that detects a fault, or keeps it from causing harm, and moves the system to a safe state. Examples are error-correcting memory, two processors comparing answers, and a watchdog timer.
Expert
Credited in the FMEDA with a diagnostic coverage per failure mode. It must itself be tested (by built-in self-test or periodic checks), or its own failure becomes a latent fault.
Explained in Automotive (Industries).