Portion of the state (or Commonwealth, if you want to be technical) of Virginia generally considered to start at the Roanoke Valley and continue to all points west, including the New River Valley, Mountain Empire and Virginia's portion of the Tri-Cities region.

If a definition just mentioning "all points west" doesn't seem to make sense to you, remember that there really is no northwestern corner of Virginia -- that became West Virginia in 1862. The northernmost point in Virginia is very near the east-west center of the state, and the state's border runs roughly south-southwest for 150 miles or so before turning more directly southwest.