Failure, Error, Fault and Defect

Terms failure,error, fault, and defect are important distinctions concepts. As a tester we should know the definitions of these four terms.

• Failure: A failure is said to occur whenever the external behavior of a system does not conform to that prescribed in the system specification.
• Error: An error is a state of the system. In the absence of any corrective action by the system, an error state could lead to a failure which would not be attributed to any event subsequent to the error.
• Fault: A fault is the adjudged cause of an error.
• Defect: Commonly refers to several troubles with the software products, with its external behavior or with its internal features.

if you are preparing for ISTQB then do not forgot  definitions of Failure, Error, Fault and Defect.