Chinese slang for "scalper," an unauthorized reseller of products. A yellow cow buys products at retail and resells them at a higher price. In China, yellow cows have bought and continue to buy hundreds of thousands of iPhones that they sell at inflated prices, and some are linked to gangs and crime syndicates.
Years ago, there were only four Apple stores in all of China, a country of 1.4 billion people. Yellow cows bought phones and sold them in the cities that had no retail Apple outlet, and the demand was off the charts. In addition, yellow cows would sign up with carriers around the world that offered the iPhone. After making the first payment, they zapped the chip to lose all traces of the carrier, and before Apple got wise to the scam, they would take the phones into an Apple store and demand replacements because they no longer worked. See
Apple in China.