In engineering, a singular documented need of what a particular product or service should be or do.
Indispensable circumstance that makes possible a specific condition.
anything indispensable; "food and shelter are necessities of life"; "the essentials of the good life"; "allow farmers to buy their requirements under favorable conditions"; "a place where the requisites of water fuel and fodder can be obtained"
something that is required in advance; "Latin was a prerequisite for admission"
required activity; "the requirements of his work affected his health"; "there were many demands on his time"
