A cascading failure is failure in a system of interconnected parts, where the service provided depends on the operation of a preceding part, and the failure of a preceding part can trigger the failure of successive parts. Redundant parts can lessen the impact of, but not prevent, a failure. Monitoring the operation of a system, in real-time, and judicious disconnection of parts can stop a cascade.
In a system with a single point of failure, loss of service can be catastrophic when that part fails.
Some classic examples of system failure due to cascading failures can be found in wide-area power outages.