Software engineering is the application of engineering to the design, development, implementation and maintenance of software in a systematic method.
Typical formal definitions of software engineering are:
"research, design, develop, and test operating systems-level software, compilers, and network distribution software for medical, industrial, military, communications, aerospace, business, scientific, and general computing applications."
"the systematic application of scientific and technological knowledge, methods, and experience to the design, implementation, testing, and documentation of software...