Derbies are a type of event that involve competition between two parties. The term is most commonly used to refer to horse races, but can also be used to describe other types of competitions such as hat derbies. A hat derby is a competition in which participants compete to see who can wear the most outrageous hat. The most popular type of hat for this type of competition is the bowler hat, which is a type of hat with a round crown and a brim that curves down at the sides. Horse races are another type of derby, in which horses compete against each other in a race.