A troy ounce is a unit of weight commonly used to measure precious metals like gold, silver, and platinum. It is part of the troy weight system, which dates back to the Middle Ages and was originally used in the trading of goods. One troy ounce is equivalent to approximately 31.1 grams. Unlike the more common avoirdupois ounce, which is used for everyday items, a troy ounce is slightly heavier, with 12 troy ounces in a troy pound. This system helps standardize the trading and valuation of precious metals in the global market, making it easier for investors and traders to understand prices.