when a girl puts that delightful arch in her back, and sticks her ass out in a erotic/sexually suggestive manor, often accompanied by a "booty dance", that brings shear delight to the males species.
"did you see her back that ass up, playboy? it almost brought a tear to me eye, and a 2x4 to my pants!"
"did you see lucy liu bending over in the drive-thru scene in charlies angels?? ddaaaaaaaaamn, it was delightful! that the essence of female perfection!"