difference between bug and defect - bug vs defect

In this article, We will learn the difference between bug and defect, What is a bug, defect, error, and failure.

In general, we use these terms in software testing whenever the system or application acts abnormally, sometimes we call it an error, sometimes bugs, and so on.

Very common to use these terms during the SDLC (software development life cycle). They seem similar to each other. But there are a few differences between bugs, defects, and errors that we need to understand.

What is a Bug?

In software testing, a bug is a deviation of the customer requirement, in simple language we can say deviation between the expected result and the actual result in an application or in a module that is found by the testing team during the testing period.

What is bug in software testing?

What is a Defect?

If the functionality of an application is not working as per the customer requirement is known as a defect, It is found during the development phase while unit testing. Like By giving wrong input may lead to a defect or Any error in code may lead to a defect.

What is an Error?

An error in software testing refers to a slip-up, misunderstanding, or mistake made by a software engineer. In the category of a developer, we include software engineers, analysts, programmers, and testers. For example, a developer may misunderstand a design notation, or a programmer might type a variable name incorrectly – leading to an Error. It is generated because of the incorrect login, loop, or syntax.

What is a Failure?

Once the software is completed and delivered to the customer and if the customer found any issue in the software then it is the condition of failure of the software.

In other words, if an end user finds an issue in the software then that particular issue is called a failure.

Difference between Bug and Defect

A bug is a deviation from the customer’s requirement. The functionality of an application not working as per the customer’s requirement is known as a defect.
The bug is found by the testing team. The defect is found by the development team.
Reason Behind Bug:

  • Missing Coding
  • Wrong Coding
  • Extra Coding
Reason Behind Defect:

  • Giving wrong input may lead to a defect.
  • Any error in code may lead to a defect.
The following list includes different types of bug:

  • Logic bugs
  • Algorithmic bugs
  • Resource bugs
The following list includes different types of Defect:
Based on priority:

  • High
  • Medium
  • Low

And based on the severity:

  • Critical
  • Major
  • Minor
  • Trivial


A simple diagram makes you understand.

Error/mistake, bug/defect, failure diagram

So we can say all terms depend on each other.

We can say that a mistake made by a programmer during coding is called an error, an error found during the unit testing in the development phase is called a defect, an error found during the testing phase is called a bug and when an error is found at an end user’s end is called as the failure.

Read Also:

1) Best Bug/Defect Tracking Tools

2) Bug Life Cycle in Software Testing

Jatin Patel

I have completed an MCA(Master of computer applications) from Jawaharlal Nehru University, New Delhi, and working as QA Engineer in QACraft. In my free time, I like bike riding, watching movies, and cooking.