Exchange traded commodities (ETCs) are open-ended debt securities based on commodities. Most ETCs are based on commodity derivatives, and are secured either by an actual, physical commodity (precious metals held by the issuer, for example) or by derivatives.
The value of an ETC matches the value of its underlying commodity. If the value of the commodity goes up, the price of the ETC goes up, and vice versa. ETCs are traded on stock exchanges and over the counter (OTC).