Distinctions between "Goods" and "Commodities"

The term "good" in this sense is kind of a squishy term. A commodity is simply something that can be bought and sold. Futures contracts are commodities, as are financial instruments which may be abstract in the extreme. Often these are called products. The Gross Domestic Product includes goods and services. But goods are definitely distinct from services. Whoever said commodities are goods is probably restricting the definition to to material things, but that's a distinction of convenience, not an absolute definition.

A commodity is a good where all the items are common and interchangeable. If you are buying art or cars then one car or pickled shark differs from the next.

Commodities can be traded easily because there is no difference in the items. Oil of a certain grade (eg Brent crude) is interchangeable, you don't have to see the particular barrel you are buying - the same with minerals, wheat, pork bellies and frozen orange juice.

As reported by the NOAD, the meaning of goods used as noun is:

merchandise or possessions
• (British) things to be transported, as distinct from passengers

The meaning of commodity reported by the same dictionary is the following one:

a raw material or primary agricultural product that can be bought and sold, such as copper or coffee
• a useful or valuable thing, such as water or time