http://en.wikipedia.org/wiki/Waist–hip_ratio
"Waist–hip ratio (WHR) is the ratio of the circumference of the waist to that of the hips." in other word that's a number to describe the sexual actractiveness of a woman
if you took Isis Taylor who is 34C-26-43 :
26 / 43 = 0,6047
the lower the better
basically below 0,70 that's already great but at 0,60 and below that's terrific