Free: Contests & Raffles.
Roadless area that requires walking or riding horses into. Usually allows you to get miles from nearest road access. Doesn't have to be wilderness IMO. There are places where you are allowed to use quads or side by sides or dirt bikes to access, AK for example. That is some real back county but you can ride machines all over it. I'm fine with that as long as the end result is a an area deep in the middle of nowhere that is difficult to access to the average day hunter.
I take it depending on the context. If I'm in my Jeep it means one thing. If I'm on foot it has a different meaning.
Each person that uses the term "Back country" will have there own idea of what that is. It could be as simple as driving down some Back country road.