The middle class Midwest that is typically "flown over" by scheduled airlines in their hops between their major hubs. The bounds of flyover country vary from urbanite to urbanite. People from Chicago tend to think it runs from the Mississippi River to the Rockies (and also Indiana). Bay Area, it's the San Joaquin Valley east to Chicago. New York, it's anything that is not within an hour's drive of The City.
Ray's nightmare came true: His plane made an emergency landing in Tulsa, the capital of flyover country, and his New York accent got him beaten by the locals.
What the Left refers to parts of the country that isn't Manhattan or L.A. and San Francisco.
I guess I live in fly-over country. Big deal.