Cupid's bow is a term to describe the shape of lips, usually on a woman. Lucille Ball had the perfect Cupid's Bow - if one was to look at her lips sideways, the points on the upper lip represent the handle of the bow, and the lower lip would represent the string. Many actresses from the 40's and 50's in Hollywood had the Cupid's Bow - real or not, it was a simple thing to draw in with lipliner.