Definitions and Meaning: Error, Fault, Failure and Defect

by Nataliia Vasylyna | December 6, 2011 10:00 am

Many people associate quality of a software system with a suggestion that some software troubles are estimated to happen (or not). And in the case if such troubles do occur, the negative influence is estimated to be minimal.

Clue to the correctness perspective of software quality is in the concept of defect, failure, fault, and error.


Commonly refers to several troubles with the software products, with its external behavior or with its internal features.


The incapacity of a system to conduct its required functions within clarified performance requirements.


A false, wrong step, process or data definition in a software product.


A person act that generates an erroneous result.

Consequently, the term failure refers to a behavioral deviation from the user wants or the product specification.

Fault refers to an underlying condition within software that causes failure to happen.

Error refers to a missing or wrong person action resulting in certain fault being injected into software.

Errors also include error sources such as human misunderstandings, dissensions, misinterpretation and so on.

Well, in literature failures, faults, and errors are together referred to as defects.

Software troubles or defects are generally referred to as “software bugs”. Nevertheless, the term software bug is never exactly defined, such as the various aspects of defects defined as errors, faults, and failures above.

Many people have also raised the moral or philosophical objection to the use of bug as evading amenability for something people committed.

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