A fairly simple Fanservice trope. When the camera pans to a woman, focusing on the curves of her back, it's this trope. Whether she's arching her back, or if the curves happen to be there, it's this trope. One can attain this most notably through a Walking Swimsuit Scene, Toplessness from the Back or full-on nudity.
Hello, Unknown Troper. You'll need to get known to lend a hand here.