Elegant degradation is a term used in engineering to describe what occurs to machines which are subject to constant, repetitive stress.

Externally, such a machine maintains the same appearance to the user, appearing to function properly. Internally, the machine slowly weakens over time. Eventually, unable to withstand the stress, it breaks down. Compared to graceful degradation

Fault-tolerant system

Fault-tolerance or graceful degradation is the property that enables a system to continue operating properly in the event of the failure of some of its components. A newer approach is progressive enhancement...

, the operational quality does not decrease at all, but the breakdown may be just as sudden.

This term's meaning varies depending on context and field, and may not be strictly considered exclusive to engineering.