Definition of Errors, Defects, Bugs, Failures and Problems.
All of these terms are often used interchangeably by QA Persons and they don’t feel any difference among those terms. I have a book “Managing the Software Process” witten by Watts S. Humphrey, In this book he precisely defines the distinction among Errors, Defects, Bugs, Failures and Problems.
Errors:
These are human mistakes, and their quantification often depends on an understanding of the programmer’s intentions. In the case of typographical or syntactic errors their causes are generally clear, but the nature and cause of design errors is much harder to establish precisely, particularly after the fact.
Defects:
These are improper program conditions that are generally the result of an error. Not all errors produce program defects, as with incorrent comments or some documentation errors. Conversely, a defect could result from such nonprogrammer causes a improper program packaging or handling.
Bugs:
A bug (or fault) is a program defect that is encountered in operation, either under test or in use. Bugs result from defects, but all defects do not cause bugs (some are latent and never found). With widely used software, the defects may be found many times, resulting in duplicates or multiple bugs per defect.
Failures:
A failure is a malfunction of a user’s installation. It may result from a bug, incorrect installation, a communication line hit, a hardware failure, and so forth.
Problems:
Problems are user-encountered difficulties. They may result from failures, misuse, or misunderstanding. Problems are human events as opposed to failures, which are system events.