used to describe a boy or girl of slight interest who isn't exactly qualified to date at the moment, but may come in handy later. thus one places them on the "back burner," keeping them warm (subtle flirting, etc.), until you're ready to chow down (i.e. date, talk, hang out with when one has nothing else to do, etc.)
"Yea Tom is acting like a dick tonight, but I have Joe on the backburner, I think I'll give him a call."
barn burner: can also refer to an epic and overpowering flatulent expulsion that smells so vomitous and full of vile toxic fumes that you swear could burn down or melt an actual man-made structure
Farmer: WHEW!! MAN ALIVE what is that horrid stench? Please tell me you didn't feed those cows spinach again?
Cow-hand: *holding his nose* No that was me - I've been holding in my grandma's hogmaw beancakes in for weeks!