Glossary
Defense in Depth
Defense in depth means relying on several independent layers of protection rather than one control asked to carry the entire burden — network segmentation, authentication, authorization, encryption, monitoring — arranged so that a failure or bypass of any single layer still leaves other layers standing between an attacker and the resource. No individual layer is assumed to be perfect.
The discipline this requires is resisting the temptation to treat one especially strong control as sufficient on its own. A system with one excellent control and nothing behind it is more fragile than one with several good-but-imperfect controls layered together, because the excellent control's failure is a single point where everything gives way at once.