Wingbox is a structural term.
I'm not sure there is a specific aerodynamic term for what you describe - wing-body lift would include all of the wing contribution, not just the 'carry through' term. The wing does get some benefit (or decrement, if you considered an isolated wing) from being on a fuselage (or vice versa if you prefer) but the theoretical wing planform in the fuselage is purely that - theoretical.