黄牛 (huáng niú) literally means 'yellow ox' or 'cattle' (a breed of bovine), but it has two common figurative slang senses. First, it refers to a scalper or ticket tout — someone who buys up tickets (concert, train, etc.) and resells them at inflated prices. Second, in informal speech it can describe a person who fails to show up or shirks responsibility — often used in the expression 放黄牛 ('to stand someone up'). These slang senses are more frequent than the literal animal meaning in everyday conversations. Use with caution in formal writing.