The literature provides several alternative definitions of software reliability. Among them are the following.
"Reliability is the probability that the software will perform its intended functions satisfactorily over its next run, or over its next quantum of execution time" (Stevenson, 1995, p. 450).
"Software reliability is the probability that a given software system will function without failure in a given environmental condition during a specified period of time. A software failure here means the inability to perform an intended task specified by a requirement. In software reliability, one emphasis is the analysis of failure mechanisms. Most software reliability models are analytical models derived from assumptions of how failures occur" (Pham, 1995, p. 5).
"Software reliability is defined as the probability that a software fault that causes deviations from the required output by more than a specified tolerance, in a specified environment, does not occur during a specified exposure period. There are three distinct methods of estimating software reliability, namely, on the basis of its failure history, its behavior for a random sample of points taken from its input domain, or the number of seeded and actual faults detected by the test team. Seeded faults are those that are deliberately inserted into the program at the start of the debugging phase, the details of which are withheld from the testing team" (Ralston & Reilly, 1993, p. 1242).
"Reliability is the probability that the software will work without failure for a specified period of time. 'Failure' means the program in its functioning has not met user requirements in some way…. Reliability incorporates all those properties that can be associated with execution of the program" (Musa, 1999, p. 26).
"Software reliability is the probability of failure-free software operation for a specified period of time in a specified environment" (Pan, 1999, p....