Difference between Error, Fault/Defect/Bug & Failure

• Difference between Error, Defect/Bug & Failure :-

Error :- Any incorrect human activity or action that produces a problem in the system is called and Error.

Fault/Defect/Bug :- Deviation from expected behavior to the actual behavior of the system is called Defect/Bug.

Failure :- The deviation identified by the end-user while using the software or system is called Failure.

Note :- [Bug is nothing but a technical slang used for a defect..]  

• Reason of defects in Software :-

1. Incorrect Requirement
2. Wrong/Poor Design.
3. Poor coding.
4. Complex Business Logic.
5. Complex Technology.
6. Work Pressure.
7. Frequently changing in Requirements.