I have always understood "dried in" to mean that the building envelope is complete, i.e. all sheathing for walls and roofs, windows and doors.
Also, the HVAC system should be in place.
The term implies that interior finishes can be installed without exposure to the elements.
Normally the roof is 100% complete, but exterior finishes such as paint or siding may not be complete.
I wouldn't think there is a formal definition anywhere.