The term 'Belles of the Ball' is a phrase used to describe young women who are the most attractive and popular at a social event. The crossword solution for this term is 'DEBS', which is an abbreviation for 'DEBUTANTES'. DEBUTANTES are young women who are presented to society at a formal ball, usually in their late teens or early twenties. They are typically from wealthy families and are expected to dress in formal attire and follow certain etiquette. As such, they are often referred to as the 'Belles of the Ball'.