Not exactly suburban, yet not exactly rural. An example of a sub-suburban area is like there are houses every 300 feet, corn fields, one farm, wide horse pastures, prairies, one Walmart, a couple of paved roads, possibly a highway, two or three schools, and a McDonald's. All within an area of at least 100 square miles.
John: God dammit, I live in a suburban area.
Kate: I live in a sub-suburban area!
John: Oh sweet, lets fuck and raise enough children to fill up an entire school bus!
Kate: Fuck yeah, and give me a beer as long as your at it!
John: Here you go, and happy 18th birthday sis!
Kate: Thanks daddy!