The part of the body posterior to the abdominal cavity, thus including the caudal peduncle and the tail fin; also used for the tail fin alone.
Birds: Feathers attached to the pygostyle and extending from the rear of the bird. The tail adds stability when walking and in flight (though birds can fly without it), aids in braking for landings, acts as a brace when climbing, and may be used for display in courtship.