What is considered as an commodity?

What is considered as an commodity?
A commodity, in the financial market context, will normally mean anything sold as contracts for a particular quantity on a commodity exchange somewhere in the world. Many commodity exchanges are electronic (or online) some still have a "floor" where the contracts are auctioned. Normally a producer will create a contract to deliver x number of units on x date, 5000 bushels of corn on Dec 2013. The producer has the actual commodity.

The commodity might be oil, gasoline, diesel fuels, natural gas, orange juice, wheat, corn, barley, gold, silver, dollar, yen, marks anything with a value that changes and comes from multiple suppliers (mines, oil driller, farmers, banks, governments, etc,)

Someone, either a speculator or an actual user of the corn will bid on that contract. If something happens to make that corn more valuable (maybe a bad crop year) the speculator might sell it at a higher price since they don't need the corn. A consumer, perhaps a bakery, need the real corn and bought the corn before the price went up so they benefit from the lower price they got earlier. It get very complicated with options to purchase, etc. Many commodity markets will respond quickly to news of freezes, oil discoveries, refinery capacity, less planted and many other factors. One purpose of the commodity exchange system is to keep the price from making wide swings on a daily basis.