Difference Between Error, Mistake, Fault, Bug, Failure, Defect.

If a tester is testing a software, s/he might come across several terms like failure, defect, bugs, mistakes, fault, error, etc., which are used by them interchangeably. However, have you ever wondered, whether these terms are synonyms of one another or do they specify different aspects of software testing process? Well, as an answer to this question, here is a detailed differentiation of all these terms, which will help us differentiate them from one another.

What is the Difference between Error, Mistake, Fault, Bug, Failure, & Defect?

The terms- error, mistakes, faults, bugs, failures, and defects are used interchangeably by the majority of people around the world, but they signify and represent different aspects of the software. These terms are an integral part of the software testing process and without detecting and identifying them the team of testers cannot validate the quality, effectiveness, functionality, and more of the software.

All these discrepancies impact the system differently, have a distinctive quality and are thoroughly different from one another. From the reason of their occurrence in the software to the steps taken to prevent them, majority of the aspects related to these terms are different. Therefore, to help you understand the difference between these components of the software, here is a detailed discussion on the same.

Error & Mistake:

During the process of software testing, errors are the most basic discrepancies found by the team of testers. These are the mistakes made by the software developer or programmer, while preparing the code or design of the software. Errors are mainly a deviation from the results expected by the team, which further changes the functionality of the software.

Reasons Error & Mistakes:

The reasons for these errors and mistakes are misconceptions or misunderstanding on the part of the software developer. Other reasons for errors and mistakes in the software are:

  • Because of wrong login, loop, and syntax.
  • Mistakes in the program.
  • Confusion in understanding the requirements of the software.
  • Miscalculation of some values.
  • Misinterpretations and issues in coding.
  • If a developer is unable to successfully compile or run a program.
  • Mistakes in design or requirement activities.
  • Discrepancy between actual and expected results.

Ways to Prevent Errors & Mistakes:

  • Improve software quality with code and system review.
  • Identify issues and prepare appropriate mitigation plan.
  • Verify fixes and validate their quality and accuracy.
  • Indulge in thorough testing.
  • Adopt effective software development methodologies.


Introduced in the software because of an error, fault is another discrepancy found by the team of testers during the process of software testing. Unlike error, the reason for a fault to occur while implementing the software is not because of a miscalculation of some value or discrepancy between actual and expected result, but is merely a manifestation of an error in a software. Moreover, a fault in the software system inhibits it from performing its intended function and forces the system to act in an unanticipated manner.

Reasons for Faults:

Faults in a system can be raised because of various reasons, few of which are mentioned here:

  • Discrepancy or issue in the code that causes the failure of the system/program.
  • Caused by an introduction of an incorrect step, process, or data definition.
  • An anomaly or irregularity in the software, which makes the software behave in an incorrect way and not as per the stated requirements.

Ways to Prevent Faults:

  • Implementing thorough code analysis.
  • Peer review.
  • Measure functional requirements.
  • Validate the accuracy of software design and programming.


Bugs are the most integral part of a software system and can be termed as the errors, flaws, and faults present in the computer program that impact the performance as well as the functionality of the software can cause it to deliver incorrect and unexpected results. These not only impact the performance of the software, but also cause it to behave in an unanticipated way.

Reasons for Bugs:

From errors and mistakes made in the source code of the software, to issues and flaws found in the software design, the reasons for bugs to be introduced in the software system can be many, which are defined below:

  • Error or flaw found in the development environment of the software.
  • Issue in the software or hardware that leads it to malfunction.
  • Discrepancies in the Operating System used by the program.
  • Few bugs are even caused due to incorrect codes produced by compilers.

Ways to Prevent Bugs:

  • Adapting innovative and effective development methodologies.
  • Offering programming language support.
  • Analyzing the code thoroughly.
  • Test-driven development.

ThinkSys Advertisement


When a software is incapable of performing the required functions and is offering results that are not adequate and far from the expected results, then it is termed as a failure. These failures are incorrect external behaviour that leads a software to deliver services that are not in compliance with the specifications.

Reasons for Failures:

Failures usually occur when a defect present in the system is executed by the team, which forces it to produce unpredicted and unanticipated results and function inappropriately. Other reasons that lead to the failure of the software are:

  1. Human Error: Errors and mistakes made by the human while interacting with the software and by providing wrong or incomplete inputs.
  2. Environmental Conditions: Another common reason that forces the system to fail are the environment conditions. These impact the hardware and force it to fail. Additionally, it changes the various environment variables.
  3. Users: Failures may also occur in the system if the user tries to perform operations that can harm the functionality of the software. Moreover, they can also execute actions with the intention of breaking the system, which will further lead to failures.
  4. System Usage: Failures might also arise due to errors in the way system is being used.

Ways to Prevent Failures:

  • Identify and analyze errors and issues.
  • Adopt effective preventive techniques.
  • Ensure re-testing.
  • Revise and revisit specifications and requirements.


If the actual result of the software deviates from the one expected and anticipated by the team of testers, while testing the software, then it results into a defect. Defects, are therefore, defined as any deviation or irregularity from the specifications mentioned in the product functional specification document by the client or any other stakeholders of the project. These are the discrepancies and issues in the software, found during the process of testing, that impact its functionality. Moreover, defects are errors found after the application goes into product.

Reasons for Defects:

Defects in the software can hinder the functionality as well as the performance of the software. Hence, it is important for us to know the various reasons that cause defects to occur in the system, some of which are mentioned below:

  • An error in coding or logic that impacts the software and causes it to malfunction or perform in an inaccurate manner.
  • Any deviation from the customer requirements also leads to defects in the software.
  • Troubles and mistakes in the external behaviour and internal structure and design.
  • Providing wrong and inaccurate inputs.

Ways to Prevent Defects:

  • Peer review.
  • Adopting various efficient programming techniques.
  • Performing regular code reviews to assess its quality and accuracy.
  • Use of effective and accurate software development methodologies.

ThinkSys Advertisement
ThinkSys Advertisement

Difference between Error, Mistake, Fault, Bug, Failure, & Defect Infographics:

Dont Forget to share our Infographics

Difference between Error, Mistake, Fault, Bug, Failure, & Defect

Conclusion :

With the assistance of above discussion, we can easily conclude that the various issues and discrepancies found during the process of software are interdependent and connected to each other. Usually, occurrence of one leads to the introduction of other, which together impacts the functionality of the software and leads it to deliver unexpected results and services, which are not in compliance with the specified requirements. Though all these discrepancies- errors, mistakes, faults, bugs, failures, and defects -hamper the quality and performance of the software, but they influence and modify different parts of the software and vary from one another immensely.

Get New Content Update
Popular Posts
Dec 07, 2020
Dec 07, 2020
Dec 07, 2020


ThinkSys Advertisement


App development ad thinksys