Futures are contracts that require delivery of a commodity (or currency in the case of the exchange market) of specified quality and quantity, at a specified price agreed upon today, on a specified future date.
There is a large secondary market in futures, meaning they can be bought and sold, much like shares of stock. Futures exist for a wide variety of goods, particularly from the agricultural and mining industries. Futures also exist for currency, but should not be confused with Forward Contracts. The latter are algorithmically priced, whereas Futures prices are strictly market driven.