Please pardon my ignorance - what's the difference?
I've never thought in these terms; we use highways to get from A to B a fair amount, however when we have the time (which is most of the time on a "big trip") we try to get off the highways onto minor roads (secondary, tertiary, etc.). We enjoy wandering on what we call back roads, trails, tracks, and occasionally where there's nothing you could call a track, but I've assumed that these terms are essentially interchangeable. I suppose that a back road is probably one which has more traffic than a track, however please educate me.