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.

A geological fault is a crack or joint between two blocks of earth (usually tectonic plates) that are moving or have moved relative to each other. Earthquakes often occur along faults.

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.

3. In power systems, an unintentional short-circuit, or partial short-circuit, between energized conductors or between an energized conductor and ground.

Source: from Federal Standard 1037C and from MIL-STD-188