At first glance, a commodity is a product that is nearly-identical to others in its class and can be bought or sold from different buyers and sellers with an understanding that you are buying or selling the functionally the same product. Under this definition, A1 corn is a commodity–if you buy A1 corn from Farmer A, you can assume it’s functionally identical to A1 corn from Farmer B. In contrast, a pumpkin pie is not a commodity–there are substantial differences between the pumpkin pie made by Company A and the pie made by Company B. Traditionally, commodities have been raw materials (like metals) or primary agricultural products (like wheat or pork bellies).
However, the official legal definition of a commodity is substantially more expansive. The Commodity Exchange Act (CEA) defines a commodity as any “goods or articles…and all services, rights, and interests… in which contracts for future delivery are presently or in the future dealt in”. The CEA lists two exceptions to this definition (movie box office futures and onions) but in general the idea is that a commodity is more than just “a bushel of barley” or “a barrel of oil”. The CEA also includes events as commodities, which are defined as an occurrence or extent of an occurrence that is outside the control of the relevant parties to the contract and “associated with financial, commercial, or economic consequence”. Measures of economic activity–such as interest rates or inflation measures–also fall under the CEA’s definition of commodity.