Software engineering is a branch of engineering that deals with the development of software. Software generally refers to the programs used by computers; technically, it is the collection of codes, documents and triggers that do a specific job and fulfill a specific set of requirements. The development of software employs the best practices, principles and methods of engineering and computer programming.
If you are curious about what is software engineering, put simply, software engineering is the application of engineering practices and principles to the field of software development.