In document ISO/CD 10303-226 fault is defined as an abnormal condition or defect at the component, equipment, or sub-system level which may lead to a failure.
In telecommunication, the term fault has the following meanings:
1. An accidental condition that causes a functional unit to fail to perform its required function.
2. A defect that causes a reproducible or catastrophic malfunction.
Note: A malfunction is considered reproducible if it occurs consistently under the same circumstances.