The term 'Old Continental Coin' refers to a type of coin known as a ducat, which was used in Europe from the Middle Ages until the early 20th century. The ducat was a gold or silver coin that was widely accepted as a form of currency throughout Europe. It was also used as a unit of account and was often used to pay taxes and fees. The ducat was a popular coin among merchants and traders, and it was even used as a form of payment for international trade.