Software engineering is the application of engineering to the development of software in a systematic method.Notable definitions of software engineering include:

"the systematic application of scientific and technological knowledge, methods, and experience to the design, implementation, testing, and documentation of software"—The Bureau of Labor Statistics—IEEE Systems and software engineering - Vocabulary
"The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software"—IEEE Standard Glossary of Software Engineering Terminology
"an engineering discipline that is concerned with all aspects of software production"—Ian Sommerville
"the establishment and use of sound engineering principles in order to economically obtain software that is reliable and works efficiently on real machines"—Fritz BauerThe term has also been used less formally:

as the informal contemporary term for the broad range of activities that were formerly called computer programming and systems analysis;
as the broad term for all aspects of the practice of computer programming, as opposed to the theory of computer programming, which is formally studied as a sub-discipline of computer science;
as the term embodying the advocacy of a specific approach to computer programming, one that urges that it be treated as an engineering discipline rather than an art or a craft, and advocates the codification of recommended practices.