What is Agio?

Legal Definition
Aggio. This term is used to denote the difference of price beteen the value of bank notes and nominal money, and the coin of the country. – Encyc.
-- Bouviers Law Dictionary
Legal Definition
In commercial law. A term used to express the difference in point of value between metallic and paper money or between one sort of metallic money and another. McCui. Diet
-- Black's Law Dictionary
Legal Definition
Agio (Italian aggio) is a term used in commerce for exchange rate, discount or premium.
-- Wikipedia