Glossary
Graceful Degradation
Graceful degradation is a system's deliberately designed, reduced-capability behavior when a dependency it relies on becomes unavailable — continuing to serve what it safely can, rather than failing completely or hanging indefinitely waiting for a dependency that isn't coming back soon. For a relying application whose identity provider goes down, this might mean already-authenticated sessions continue working uninterrupted while new logins are blocked, rather than every single user, logged in or not, being locked out simultaneously.
Designing for this deliberately, in advance, is what separates graceful degradation from an accidental partial outage: the reduced-capability behavior has to actually be planned and tested, or what happens during a real dependency outage is whatever the system happens to do by default, rather than what its designers actually intended.