Error, Defect, Fault, Bug, and Failure

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Safa Emhemed
·Aug 18, 2022·

2 min read

Error, Defect, Fault, Bug, and Failure

Most of these terms- error, defect, fault, failure, and bugs are used interchangeably but there is a difference between them. Some of these terms are very much different from others. We will see these terms in detail one by one.


An error is a mistake made by humans that leads to a discrepancy between the actual and the expected result.


A defect is a problem in the functioning of a software system during testing. ISTQB defines a defect as “A flaw in a component or system that can cause the component or system to fail to perform its required function, e.g., an incorrect statement or data definition.”


A fault is an incorrect step, process, or data definition in a software product.


A bug is a flaw in a software system that causes the system to behave in an unintended manner.


A failure is the inability of a software system to perform its operations within the specified performance benchmark. As per ISTQB, “a defect, if encountered during execution, may cause a failure of the component or system”.

Final Words:

So, we can say that a mistake made by humans during coding is called an error, an error found during the testing phase is called a defect, a defect to be resolved by the development team is called a bug and when a build does not meet its specifications then it is termed as failure.

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