Definitions

• Requirement - is a statement that is in principle testable



• "The program has an average response time of t seconds" - Testable



• Specification - is a statement that in principle is provable



• "The program satisfies the predicate P(x)" - Provable



• "The program has a good response time " - Vague



• Failure - Deviation of a software system from its requirement



• Fault - A software defect that can cause a failure



• Error - Action by a software developer that results in the introduction of a fault into a software system



• Problem - A difficulty in the use or understanding of a software system



• Robust - A software system is robust if it is fault-tolerant or failure-tolerant