What is the difference between Error, defect,fault, failure and mistake

Questions by shyam_meghansh   answers by shyam_meghansh

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manish soni

  • Sep 11th, 2006

hi to all,

Error/bug/defect/mistake-->  are human intraction which produce an incorrect result.

Fault--> Fault is a stage of software which is caused by an error/bug/defect/mistake.

Failure--> It is a deviation of software from its expected delivery or service.

For eg. 

you are driving a car and you are on road while on driving now there is two way on the road

1) left--> mumbai

2) right--> delhi 

now you have to go to delhi it means you have to turn the stearing to the right, but by mistake you turn the stearing to the left, from that position that is called as "Error" because human intraction is there. and now Fault is there till you will not reach the mumbai, but when you reach mumbai that is a final stage which is called "Failure" becoz you had to reach delhi but now you are in Mumbai.


  • Oct 4th, 2006








  • Oct 11th, 2006


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Kumar Surapaneni

  • Jul 11th, 2007

Error: Mistake made in Coding or Mistake made by a Programmer the may result in a Program .
Defect : Variance between Expected and Actual Reault .
Failure: in ability of  a system to perform the Functionality according to its Requirements.
Fault: is a condition that causes the software to fail to perform its required function.

Error: Errors are basically the deviation from the requirement, caught by testers and caused by misunderstanding of the Developers.

Bug: If the Error found by testers are accepted as error by Developers. Then the error will called Bug.

Defect: Suppose any product/software is currently running as a beta version in the market/client side. Any issue currently caught in that application that are deviating the actual result from the requirement, will taken as Defect.

Fault: When the product/software successfully launched in the market and running properly but due to any reason if it works unexpectedly is called Fault.

Failure: If the product fails to full fill the requirement, then it is called Failure.

thainese victoria

  • Jul 14th, 2011

defect:when the error found something against to the requirements from the customer
bug:when the defect accepted by the developer is bug
error:error can be missing,extra,invalid implementation of the requirement
missing:requirements are missing
extra:requirements added extra which is not needed to the customer

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  • Jan 19th, 2012

What is bug?
I did not get the actual difference between bug and defect still.

Could u explain all with examples?


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koteswara rao

  • Feb 22nd, 2012

Fault - is the condition which causes the software fail to perform the action
Failure - is an event caused by an error
Error - difference between exist in the coding
Defect - difference between expected and actual in the testing course/ phase
Bug -- accepted the above said defect by developer then called as bug

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M Ravi Shankar

  • Mar 12th, 2012

Defect is a deviation from the requirements specifications.
For example there is Login feature, accordingly to requirement it shouldn't accept any special characters but developer has missed this the requirement and developed. While doing functional testing you found that the login text filed is accepting special characters, it is called as Defect.

Bug: It is a informal name given to defect.

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Defect/Bug/Fault : A flaw in the system/application/component that can cause it to fail is termed as Defect/Bug/Fault. Defect, Bug and Fault are all the same.

Error/Mistake: A wrong input or erroneous input by a user leads to error. Error and Mistake are the same.

Failure: If the END PRODUCT deviates from the EXPECTED PRODUCT i.e. if there is a difference between the END PRODUCT and what the Client wanted, it is a failure

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  • Apr 19th, 2012

error:- error is nothing but programing error,which is detected by the developers. programing errors like syntax error,semantic errors,
defect:-defect is expected not equal to the actual , means if developed code is not match with clients expectations, defect is detect by the testers

failure:-after compilation of all coding ,testing the software code give to the client. when ever get problem with that developed s/w while using by client ,then this will said as failure

defect is also known as fault,mistake

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  • Jun 3rd, 2012

Bug: A human committed mistakes in pre production or in development process called Bug

Defect: Deviation between the expected and Actual Results Called
Defect. Usally we found these in post production.

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  • Jun 9th, 2012

RROR=represents mistake made by human.a diff between computed ,observed or measured value or condition and true specified or theoretically correct value or condition..an incorrect action which produces problem in a system

FAULT= it is a result of error.an incorrect step process or data definition in computer prog which causes the program to perform in unanticipated manner

FAILURE=occurs when fault executes..the inability of system to perform its required function within specified requirements.

DEFECT=Failure in normal function.deviation from expected behavior to actual behavior..defect is deviation from requirements.problem in algorithm leads to failure

BUG=is evidence of error in software.a fault in a program which causes program to perform in unanticipated manner

when defect is reported to developer team they will review those defects .If they accept those defects then data becomes bug in development environment.

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priyanka agarwal

  • Jul 21st, 2012

fault: fault can be happened at lower level.when a software is launched to the market and running properly but suddenly one or more applications gets corrupt then it is a fault.

failure: failure can be happened at higher level. when the running system is fully corrupted and does not work at all then it is a failure.It occurs when fault executes.

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Error (Mistake): It’s a human action producing an incorrect result. When programmers make errors, they introduce fault top program code.

Fault (bug/defect): A manifestation of human error is software. Only Faults in software cause it to fail. Faults may be caused by requirement, design or coding error. Software faults are static; they are the characteristics of the code they exist in. Once injected within system they remain there until exposed by a test and fixed.

Failure: A deviation actual behavior of the software from its expected. Failure occurs when software does the wrong thing. It’s a deviation of the software from the functional Specification or Product Requirement

An human error within program code introduces software fault with the code & causes software failure.

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prashansa raj

  • Aug 17th, 2012

Error: computation of one or more incorrect results by a computer.
Bug: is a fault in a program which causes the program to perform in an unanticipated manner.
Fault: an incorrect step, process or data definition in a computer program which causes the program fail to perform action.
Failure: inability of a system to perform a given function within given limits.

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Manas Pradhan

  • Aug 21st, 2012

Error- A human action which produces incorrect result and required investigation

Bug/Defect/Mistake- They all mean the same - a flaw in a system or in a componeant which makes the system fail

Failure- a bug/defect when missed out by testing team and found by a customer at production environment and already affect the business

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  • Oct 4th, 2012

Error:it is at the developers end when an application fails to run.
Defect:Same problem when occurs at the testers end,it is named as Defect.
Failure:Same problem occurs at the end users application.

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Nikita jain

  • Oct 10th, 2012

Error (mistake) A human action that produces an incorrect result.
Defect (bug, fault) 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 defect, if encountered during execution, may cause a failure of the component or system.
Failure Deviation of the component or system from its expected delivery, service or result.

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  • May 3rd, 2014

a mistake in coding is called error this found by tester is called defect this found by development team then it is called bug this leads failure

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  • May 28th, 2014

Priority is always decided by developer and severity always decided by tester

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  • Jun 1st, 2014

defect -- slight deviation from requirements or if an issue is identified by tester is called as defect

failure -- if the same defect is not identified bt testing team,then the s/w will be deployed--if cx identifies that issue,it is called as failure

bug -- informal name of defect or if development team approves the issue identified by testing team,it is called as bug

error -- anything that is stopping to execute/run the program(s/w) is called error

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  • Jun 9th, 2014

Error-is the programming error should be detected by the Developers before giving the code for testing

Defect- the discrepancy between actual expected behavior or in other words defect is the functional deviation from the SRS or any functional docs.

Failure-Defects will cause failure of the system.

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Naveen Kumar kaderu

  • Mar 15th, 2015

“A mistake in coding is called error ,error found by tester is called defect, defect accepted by development team then it is called bug ,build does not meet the requirements then it Is failure.”

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Neha Mutalik

  • Dec 21st, 2015

Fault: An incorrect step, process, or data definition in a computer program which causes the program to perform in an unintended manner.

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.

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Ibrahim Ramadan

  • Jan 15th, 2016

What is an error?
Error is deviation from actual and expected value.
It represents mistake made by people.
What is a fault?
Fault is incorrect step, process or data definition in a computer program which causes the program to behave in an unintended or unanticipated manner.
It is the result of the error.
What is a bug?
Bug is a fault in the program which causes the program to behave in an unintended or unanticipated manner.
It is an evidence of fault in the program.
What is a failure?
Failure is the inability of a system or a component to perform its required functions within specified performance requirements.
Failure occurs when fault executes.
What is a defect?
A defect is an error in coding or logic that causes a program to malfunction or to produce incorrect/unexpected results.
A defect is said to be detected when a failure is observed.

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Pradeep Singh

  • Jul 1st, 2016

A mistake in coding is called ERROR, Error found by tester is called DEFECT, Defect accepted by developer is called BUG, If build does not meet requirements then it is FAILURE.

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  • Aug 19th, 2018

explanation is tooo good thank u soo much

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