In engineering, a fault is a defect or problem in a system that causes it to fail or act abnormally.
The ISO document 10303-226 defines fault as an abnormal condition or defect at the component, equipment, or sub-system level which may lead to a failure.
But the rate at which a particular fault occurs among a large number of units often can be predicted with significant accuracy.
Manufacturers often accept random faults as a risk if the chances are virtually negligible.
A fault can happen in virtually any object or appliance, most common with electronics and machinery.