Requirements engineering (RE) refers to the process of defining, documenting and maintaining requirements and to the subfields of systems engineering and software engineering concerned with this process.The first use of the term 'requirements engineering' was probably in 1979 in a TRW technical report but did not come into general use until the 1990s with the publication of an IEEE Computer Society tutorial and the establishment of a conference series on requirements engineering that has evolved into the current International Requirements Engineering Conference.In the waterfall model, requirements engineering is presented as the first phase of the development process.