Engineering is the creative application of science, mathematical methods, and empirical evidence to the innovation, design, construction, operation and maintenance of structures, machines, materials, devices, systems, processes, and organizations. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application. See glossary of engineering.
Computer software, or simply software, is a part of a computer system that consists of data or computer instructions, in contrast to the physical hardware from which the system is built. In computer science and software engineering, computer software is all information processed by computer systems, programs and data. Computer software includes computer programs, libraries and related non-executable data, such as online documentation or digital media. Computer hardware and software require each other and neither can be realistically used on its own.
How can it be that we have so much software that is reliable enough for us to use it? The answer is simple; programming is a trial and error craft. People write programs without any expectation that they will be right the first time. They spend at least as much time testing them and correcting errors as they spent writing the initial program. Large concerns have separate groups of testers to do quality assurance. Programmers cannot be trusted to test their own programs adequately. Software is released for use, not when it is known to be correct, but when the rate of discovering new errors slows down to one that management considers acceptable. Users learn to expect errors and are often told how to avoid the bugs until the program is improved.
Parnas, David L. (Jan 1 1985). "The Parnas Papers". SIGCAS Comput. Soc. 14,15: 27-37. DOI:10.1145/379486.379513.