The ability of maintaining functionality when portions of a system break down.

A system that is designed to fail safe, or fail-secure, or fail gracefully, whether it functions at a reduced level or fails completely, does so in a way that protects people, property, or data from injury, damage, intrusion, or disclosure. A program might fail-safe by executing a graceful exit (as opposed to an uncontrolled crash) in order to prevent data corruption after experiencing an error.