Difference between Fault, Failure and Error

Fault : An incorrect step, process, or data definition in a computer program which causes the program to perform in an unintended or unanticipated manner. It is an inherent weakness of the design or implementation which might result in a failure. A fault might be present and latent in the systems like they were in Patriot Missile failure and Therac-25 accidents. These faults lead to a failure when the exact scenario is met.

• Fault avoidance – using techniques and procedures which aim to avoid the introduction of faults during any phase of the safety lifecycle of the safety-related system
• Fault tolerance – the ability of a functional unit to continue to perform a required function in the presence of faults or errors

Failure: The inability of a system or component to perform its required functions within specified performance requirements

Error : A discrepancy between a computed, observed, or measured value or condition and the true, specified, or theoretically correct value or condition.