Difference Between Bug, Defect, Error, Fault and Failure

Several terminologies are used in the field of software development to characterise problems that can arise in software systems and applications. These phrases include "bug," "defect," "error," "fault," and "failure," yet they are frequently used synonymously, which causes misunderstanding among stakeholders and developers. In order to effectively communicate and solve problems in the software development industry, it is crucial to comprehend the differences between these phrases.

What are Bugs?

An mistake, flaw, or fault in a computer programme or system that makes it act unexpectedly or produce inaccurate or undesired consequences is known as a bug in the software development industry. Incomplete or confusing specifications, unanticipated inputs or situations, hardware or other software issues, programming errors, and other factors can all result in bugs.

From simple annoyances to major failures that might result in data loss, system crashes, or security vulnerabilities, bugs can have a wide range of effects. Software engineers utilise a range of methods, including testing, code reviews, and automated analysis tools, to find and correct flaws before they are incorporated into live systems in order to prevent defects.

What are Defects?

A software application or system defect is a different name for a bug, fault, or flaw that prevents it from operating as intended. Several things, like programming errors, design faults, or insufficient testing, might lead to defects.

Defects, like bugs, can be avoided by implementing various quality assurance procedures like testing, code reviews, and automated analysis. Software engineers must address and correct faults once they have been found in order for the system or application to function as intended.

What are Errors?

An error in software development is a mistake that a software developer makes when writing code. Mistakes can be brought about by a number of things, including a lack of expertise or experience, a misunderstanding of the requirements or the design, or just an accident.

Software engineers apply a number of approaches to avoid problems, including creating clear and succinct code, checking their work, and employing automated analysis tools to find flaws. When mistakes do happen, programmers must find them through debugging and testing to guarantee that the software operates properly.

What are Faults?

A fault in software development is a flaw that can make a software application or system malfunction or give inaccurate results. A flaw is typically brought about by a coding or design problem in the software that leads to an unexpected behaviour when the programme is run.

Software developers utilise a variety of methods to ensure that their work is strong and trustworthy, including testing, design reviews, and cautious coding procedures. When errors do arise, programmers employ debugging techniques to locate and address the root cause in order to return the software to normal operation.

What are Failures?

A failure in software development is when a system or software programme falls short of user expectations or intended requirements. Failure can happen when a flaw or defect in the software causes unanticipated behaviour, which prevents it from carrying out the intended function.

Software developers employ a range of strategies, such as thorough testing and quality assurance procedures, to guarantee that their software satisfies the intended criteria and performs dependably in order to prevent failures. When a failure happens, developers must look into the underlying reason and take the necessary steps to rectify it, such as addressing the flaw or defect that gave rise to the failure.

Bugs vs Defect vs Error vs Fault vs Failure

Let us now compare and contrast the different features of Bugs, Defects, Errors, Faults, and Failures:


  • Bug − It is a colloquial term used to describe a defect.

  • Defect − The discrepancy between actual results and anticipated outputs is known as the defect.

  • Error − Since an error is a mistake in the code, we are unable to execute or compile the code.

  • Fault − A Fault is a condition that prevents the software from doing its fundamental task.

  • Failure − If the software has several flaws, it will fail or will be the cause of failure.

Raised By

  • Bug − Bugs are reported by the test engineers.

  • Defect − Defects are found by the testers. Also, the developer addressed it at the early stages of development.

  • Error − Errors are brought up by the developers and automated test engineers.

  • Fault − Faults are caused by human errors.

  • Failure − During the development cycle, the manual test engineers discover the failure.

Different Types

  • Bug − Logic bugs, Algorithmic bugs, Resource bugs

  • Defect − Based on priority: High, Medium, Low. Based on severity: Critical, Major, Minor, Trivial early stages of development.

  • Error − Syntactic mistake, an interface flaw, mistake in flow control, mistake in error handling, Calculation blunder, Testing mistake with hardware

  • Fault − Errors in Business Logic, Logic and Functional Errors, Poor GUI Performance Issues, Security Errors, Hardware/software error

  • Failure − No categories


  • Bug − Lack of coding, incorrect coding, added coding

  • Defect − Giving inaccurate and incorrect inputs. Problems and mistakes in the internal structure and design as well as external behaviour. The software is affected by a coding or logic problem, which results in its failure or breakdown.

  • Error − Errors in the code. The Mistake of some values. If a developer is unable to compile or run a program successfully. Confusions and issues in programming. Misperception in understanding the requirements of the application.

  • Fault − An incorrect step in the initial stage, procedure, or data definition might result in a fault. Issue or inconsistency with the program. A flaw or irregularity in the program that causes it to function incorrectly.

  • Failure − Environmental condition, System usage, Human error

Way to Prevent the Causes

  • Bug − Development that is test-driven. Support for programming languages. Adjusting cutting-edge and practical development techniques. Systematising the code evaluation.

  • Defect − Using a variety of cutting-edge programming techniques. Use of fundamental and accurate software development methodologies. Performing regular code reviews to assess the quality and accuracy of the code.

  • Error − Reviewing the system and code will improve the software's quality. Find the problems and create a good mitigation strategy. Verify the fixes' accuracy and quality by validating them.

  • Fault − Peer evaluation. Evaluate the software's functional requirements. Carry out the thorough code analysis. Check the programming and design of the software.

  • Failure − Verify the retesting. Study the specifications and go over the requirements. Put existing safety measures into practise. Sort and rank errors and problems.


Understanding the terms that are used for describing software problems is crucial for software development. Although they all contain somewhat similar notions, bugs, defects, mistakes, faults, and failures have slightly distinct definitions. In contrast, an error refers to a mistake made by a developer when developing code, a bug or defect refers to a flaw or error in the software.

Updated on: 03-Jul-2023

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