Definition
Fault Tolerance is a system property that enables continued correct operation despite the failure of one or more components within defined conditions.
Human Explanation
The system can continue performing its required function even when part of it stops working.
Why it Matters
Fault Tolerance limits the immediate effect of component failure on users and supports critical systems that cannot accept service interruption.
Conceptual Boundary
Fault Tolerance does not prevent failures and is not the same as recovery after an outage. It means the architecture can continue required operation while specified failures are present.
Practical Perspective
Fault tolerance must define which failures are covered and must address detection, isolation and degraded modes; redundancy alone is insufficient when components share the same cause of failure.