A fad, commercial hook or type of propaganda in which an item which is trashy, cheap, useless and overpriced is given grandiose purpose and meaning which transparently contradicts its nature. Usually it only takes one person to notice how stupid poshlust is in order to kill it, but most people don't want to lose their sense of false-belonging so in our soft-drink-and-game-show culture they embrace new poshlust at every chance.
Jeopardy Contestant-- "I'll take words from Russia for $600, Alex."
Alex Trebek-- "The answer is: Support Our Troops stickers on an SUV, $300 jeans made to look old, and Paris Hilton trying to be like Common People."
Winning Contestant-- "What is poshlust?"