This qualifier qualifies severity of a specification, i.e., the importance it will have in the final delivery.

A severe specification will produce some deliverables that are highly expected. Such features are central objectives of the project itself. Severity is usually linked to the strength given to relevant requirements. But in some cases, severity could be a technical recommandation, out of care of the final customer.

Less severe specifications will continue to be negotiable, although lack of them will always pull the final delivery to lower quality.