Difference between Defect, Error, Bug, Fault and Failure

Defect:

While testing when a tester executes the test cases he might observe the actual test results do not match with the expected results. The variation of expected and actual result is known as defect.

• Different organizations have different names to describe this variation, commonly defects also known as bug, problem, incidents, issues.

Error:

If developers misunderstand the requirements then he should code as per his understand which leads to error.

•   Simply programming mistake is called error.

Bug:

If the defect was accepted by the developer it is called bug.

Fault:

If major functionality missed after delivering is called fault.

Failure:

If customer identify the bug in software is called failure.