What is a "commodity" when referred to as an adjective to describe a particular object?

When people describe any object (such as a career, or for instance, a computer cluster, etc) and they describe it as "commodity", what is it supposed to mean?

According to Wikipedia, a commodity is basically something that fills in a need or a want, but if that's true, then isn't everything a commodity?

Basically, what kind of connotation does the word have in everyday usage?

A commodity is a good that is treated as interchangeable with another sample of the same good in a market. Crude oil is a commodity: a barrel of light sweet crude oil trades for the same price on international markets no matter where in the world it came from or who extracted it from the earth. By contrast, cars are not a commodity, because each make and model is different. You wouldn't treat a BMW and a Chevrolet as the same thing when buying or selling cars.

By extension, the word commodity is also sometimes used to describe any class of things that can't be effectively sold based on differentiation between competitors, and must therefore be sold on a price basis alone. Computers are often called commodity items these days: there are differences between Dell and HP computers, but from the point of view of the consumer they usually aren't important enough to make the difference between buying a Dell computer and an HP computer with equivalent specs; the consumer is more likely to use price as the sole determiner. Profit margins in the computer industry therefore tend to be razor thin, with competitors trapped in a race to become the cheapest.

In general, when something is described as a commodity in this latter sense, the implication is not a good one for sellers of the commodity: if your profession is described as a commodity, it's probably going to be difficult for you to distinguish yourself from your colleagues in the job market, and your job may be a good candidate to get outsourced to another market that offers cheaper labor.

One use of the word "commodity" is to describe basic goods that can be bought and sold, such as rice, gold, etc.

But when a career or a computer cluster is referred to as a commodity, it means that it can be turned to an advantage, or bring profit, eg:

Fast-learning methods are a much sought-after commodity in our ever changing world.