What is Cornucopia?

This is a horn that Piper cuts off of Achelephus for Hercules. However, Hercules is such a jerk she can't bear to give it to him. Instead, it turns itself into a horn of plenty (cornucopia) and Piper uses it to great facility many times. She uses it to bury Hercules in fruits and vegetables, and then later, she uses it to pay tribute to the gods so that they can pass through various places unharmed.