The scope of work is the written description of exactly what a contractor will do on a job, including quantities, thicknesses, materials and exclusions.
On a paving proposal it names the area, the lift thickness, the mix, the milling depth, the tack, the striping layout and what happens to the millings. On a concrete proposal it names the thickness, the mix strength, the reinforcement, the finish and the joint spacing.
The exclusions are part of the scope, and they settle most arguments: unsuitable subgrade, utility conflicts, permits, and cars that were supposed to be moved.
A scope specific enough to build from is specific enough to bill from. When the site turns out different, the difference is a change order, and the scope is what the change gets measured against.