A fetish (derived from the French fétiche; which comes from the Portuguese feitiço; and this in turn from Latin facticius, "artificial" and facere, "to make") is an object believed to have supernatural powers, or in particular, a man-made object that has power over others. Essentially, fetishism is the emic attribution of inherent value or powers to an object.
Tuning in on TV or radio, opening a newspaper or magazine or just plain taking a stroll through the city, one can not evade the omnipresent advertising of goods and products we are promised will enrich our lives, if only we purchase them. So far, so bad. The sensoric terror of consumer society can not be evaded and therefore we have adapted to often not even consciously register the advertising messages anymore.
How else to explain the seeming obliviousness to the inherent absurdity of many ads?
Many products promise plain supernatural qualities: margarine is no longer just nutritional, it's actively helping you lose weight by the power of magical ingredients whose name you can't remember, but which sounded just scientific enough to buy it. Yoghurt is no longer a tasty dessert or snack, it's a potent potion to improve your health. And deodorants don't just mask the natural stench of your armpits; those days, it's making you literally irresistable to the opposite gender.
It's easy to mock such claims and deem yourself above falling prey to ridiculous promises, but we have to note that this form of advertisement must strike a nerve. If it weren't succesful, it would have vanished from the tools of manipulation the great advertising agencies use. It didn't. To the contrary, the attribution of traits to products they, according to common sense, just can't possess, is hegemonial in the world of advertisement.
This goes beyond outright claiming certain properties, like the food industry likes to do with imaginary health benefits of their products. Often, the association is more subtle and implied. Try finding a car advertisement that is actually about objective qualities of a car and not about associating a desired lifestyle with it. You'll be hard pressed. A sports car will subconsciously promise you vitality and power, a family car will promise you a happy family.
Entire business models rest on such attributions. There are plenty of myths about organic products that just don't stand up to the actual conditions under which they're produced. Organic food and fair trade promise you to make the revolution purchaseable. You can safely continue your saturated middle-class consumer lifestyle, all that matters is that you buy the right products. This is fundamentally the same assumption that may lead others to buy a fast car to get laid - just with more pretentious, smug moralism to back up your choice.
It works the other way round, too. Certain producers have managed to acquire such a bad reputation or get their products associated with moral qualities, that buying them makes you a bad person yourself. Try, for example, to argue with a common left-winger about the question why Coca Cola is bad, but buying a competing brand is seemingly acceptable. Or take the German clothing retailer "KIK", whose customers have become synonymous with uneducated, poor and anti-social losers to most of the German public - which happily shops at stores that sell essentially the same clothers, sometimes from the very same factories in Bangladesh.
Even those who think they have "opted out" of consumer society and are not affected by advertisement and the mass produced goods it promotes will believe in this very same "magic of things", just from a different angle. Take the obsession with hand-crafted products - which are, as a matter of quality, often worse than their mass produced counterparts. The entire premise of the DIY subculture is that products you made yourself have some inherent quality that makes them morally superior to those bought in stores. No matter the real advantages or disadvantages of a certain design, they are said to have a greater "authenticity".
Human attributes are expressed through goods.
This goes to show that the problem lies deeper than manipulation through advertisement. It's not a great plot to make us buy products. Advertisers merely pick up on a way of thinking that we have already absorbed since day one of our lives as capitalist subjects, that we are nothing but the sum of our accumulated property and our value on the market. It is only consequential that individuals, which mainly interact with each other through the things they have to offer on the market, will project parts of their humanity onto material possession.
That is the essence of fetishism in capitalist society: we have become so emotionally hollow that we have to supplant our own humanity with magic objects.