Attributes of well defined requirements -

List to for reading before define requirements:

Unambiguous: Precise and clear with only one interpretation. Consensus agreement.
Complete: Every known aspect is described.
Consistent: No contradictions, uniform terminology used.
Measurable: In terms of time and cost, can it be estimated? Can it be verified against the implemented solution?
Testable: Requirements should be quantifiable.
Traceable: Must be able to track from project inception to delivery.
Design-free: “What” not “How.”
Understandable: Able to be understood by non-technical customers, system users and developers.