1) A requirement is a subsets of the problem domain. This can be compared to the design which is a subset of the machine and focuses on the solution rather than problem. The union of the two is done through the specification.
1a) Must distinguish preferences, priorities
Figure out the requirements for this new software project.
Having all the "elements" someone would want. Such as body, with personality, and a good job, or just a low ball set of things you want to find in a mate. Rack and an ass, money and a fly ride, easy and cute, etc.
She/He has all the "requirements" to be my next Ex-(Girlfriend/Boyfriend)!