Slant Butt
This terminology is used to describe the viewpoint an individual has of the buttocks of another person. "Slope Butt" can also be used as substitue verbiage for Slant Butt. "Slant" or "slope" is used primarily to explain the degree to which a person's buttocks is convex from the back of the thigh and the base of the spine.
"My girlfriend has the perfect slant butt; the slope of it's cushion is better than memory foam or a down feather pillow."