I call backstraps the strips of meat you filet from the underside of the spine, from inside the cavity of the animal.
Loins/tenderloins are only accessible after you've skinned the animal; they run on each side of the spine on top of the animal.
In our Wisconsin camp, backstraps are the desired meat, usually consumed the day of the kill. We grill them with a simple mix of olive oil, garlic, salt and pepper. In my opinion, the finest meat on the planet.
If we have a really successful year we'll freeze a few backstraps and enjoy in the spring as part of Wisconsin Surf and Turf (fresh fried bluegills and backstrap).
After the backstraps, I agree with a lot of you; it's all delicious provided it's field dressed appropriately, cooled quickly, and prepared properly.
I call`em just the opposite- I call the tenderloins the stips of meat you cut from inside the body cavity, and the back straps are the rear top, kinda small of the back.
Whatever you call each, they`re fantastic.