Scope is the tangible outcome of project tasks
I think he considers scope to be a true sibling of cost and schedule, not above or below
Scope is not value or work but the basis of value and the result of work
This makes me think
Scope is the mapping from work to value
Scope attributes
Units: drawings, parts, etc
Effort: nominal hours, story points
Divisibility
Complexity, uncertainty
Target neutral
If customer target changes then value of scope changes but the scope is not changes
Resource Nominal
eg
Man months
Exception realistic
A way to describe a scope partial, imperfect, and rework