Working while employed at large companies, I was at times confused as to what was considered to be a requirement and how a specification differs from it. Upon reading more about it, I have discovered the absense of a precise definition of a Requirement. All explanations are vague. Please, clarify from the practical experience.
TL;DR: (if I really had to) I would use "design specification" as a superset of "requirements"
My experience is that:
- Requirement: tends to be used more commonly in the design phase of a product, and also imply a "absolute minimum".
E.g.: When people are on a drawing board and try to decide what the requirement for a new chair, they might say that a requirement is that it may be used for a person which is 100[kg], and the packaging dimension should not exceed 100x500x500[mm].
These two are the minimum requirements. Of course, if the chair can be approved for a person being 120[kg] and the packaging dimension of 80x450x450[mm], then the requirements are still met.
The specification usually refers to (and you come across it more often when talking about) the properties of the finished product.
e.g. in the case of the chair previously mentioned, the specification of th finished product, will state that it is approved for a person of 120[kg] and its packaging comes into 80x450x450[mm]. So the original "design requirements" are now irrelevant.
- Design specifications
Obviously this is the difficult one. The design specifications have to me a near identical meaning with requirement. "
The only difference I can perceive, is that the requirements are the CORE properties around which the design has to revolve around and they are closest to "being written in stone". On the other hand, the design specification usually refers to "requirements" and other not so essential parameters of the design. So, to my mind "design specification" is a superset of "requirements"