The tenderloin is a long, thin strip of meat that runs along each side of the backbone, inside the animal, in a cow or a pig. It is the softest meat on the animal, because that muscle does almost no work while the animal moves — muscles that work hard get tough, and this one barely works at all. That softness makes it expensive, and it is why beef tenderloin is what a steakhouse serves as filet mignon. It cooks fast and dries out easily, so cooks usually give it high heat for a short time. In the meat counter you will hear pork tenderloin far more often than beef tenderloin, because pork tenderloin is cheap and small, a common weeknight dinner. There is a second use, and it is a strange one worth knowing because it appears in books and news. In American English, 'the Tenderloin' is a name for a rough district of a city — the most famous is in San Francisco. The story usually told is that police posted there could afford better cuts of meat because of the bribes, so the name stuck; that is the common explanation, though not everyone accepts it. Either way, when an American says 'the Tenderloin' with a capital T, they mean a neighbourhood, not dinner.