Physical substances, which are interchangeable with another product of the same type such as food, grains, and metals, are commodities which investors are trading them through futures contracts. The price of the commodity is subject to supply and demand. More generally, a product which trades on a commodity exchange; this would also include foreign currencies and financial instruments and indexes.
Commodities have the following properties.
1- it is a good that is usually produced traded by many different companies. 2- it is uniform in quality between companies that produce and sell it. Meaning, one cannot tell the difference between one firm's product and another.