Duck fat, also referred to as Schmaltz, is a light colored fat typically rendered from the skin and fat of the duck. It is a common French cooking ingredient used for perfect for confit and general sautés.
You can mix duck fat with blanched pounded garlic to make Gascony butter. The butter is used to flavor soups and cassoulet. You can roast vegetables with duck fat to enhance the flavor. French fries made with duck fat (Duck Fat Fries) are popular in many restaurants.
If you are seeking a substitute for duck fat you can render your own (it takes a lot of time and effort):