Difference between Bug and Defect

In this post, we will learn difference between bug and defect.

In the software testing it is very common to use these terms during software development life cycle. These terms seem similar to each other. But there are few differences between bug, defect and error which we need to understand.

What is a defect?

A variation between expected result and actual result is called a defect or if functionality of the application is not working as expected then it is a defect. They can be found by developers in development phase while unit testing.


What is a bug?

If functionality is not working as expected while testing phase then it is called bugs.

There are different types of bugs which are as follows –

  • Functional Errors
  • Missing Errors
  • Compilation Errors
  • Runtime Errors
  • Logical Errors

Above given errors lead to bugs

Note: As we know defect and bugs both terms are used when we found issues in the application, but the difference is depends on stage they are caught at. If the issues are discovered in testing life cycle then it is known as bugs and if issues are found in development phase then they are classified as defects.


What is an Error?

It can be done by any programmer. It is a programming mistake generated due to wrong syntax, loops etc.


What is a failure?

Once the application or software delivered to the customer and the defect is found by customers or end user then it is known as failure.

“When the defect is found by end user then it is called as failure”.

Causes of failure:

Human mistake lead to Failure

Environment Conditions.

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Difference between Bug and Defect


FAQ— Frequently Asked Questions

Q1. What is fault in software testing?

A fault is introduced into an application as the result of an error. Because of this the application may behave incorrectly.

Q2. Is a bug a defect?

No, if a fault found in testing phase by testers then it is known as bug and if a fault is found in development phase by developer in unit testing then it is called defect.

Q3. What is bug defect life cycle?

Bug life cycle is also known as defect life cycle. It is a process in which defect goes in different stages in its entire life.

Q4. When should you close defect?

After retesting if bug is no longer exists then we can close the bug.

Q5. Difference between bug and error?

Bug: If an error is found in testing so that functionality is not working as expected then it is called bug.

Error: It can be a programming mistake by a programmer due to wrong syntax etc.


In this post, we have covered ‘Difference between Bug and Defect’ and about Error/failures.

Final word, Bookmark this post  ‘Difference between Bug and Defect for future reference.

If you have other questions or feedback, the comment section is yours. Don’t forget to leave a comment below!


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