it is in the shape of a bow, and lips are the 'love'(cupid) of your face.
hence the name "cupids bow"
some cupids bows dip loads more... and almost go down to the bottom of the top lip (where the lips meet).
there are also lips that do not have a cupids bow, so they would just be rounded at the top with no dip so it would be like a mirror image of the bottom lip.
person b: thanks, yours are nice too
person a: well not really, i dont have a cupids bow
person b: so...