A troy ounce is a unit of measurement for precious metal weight that dates back to the Middle Ages. It is used to weigh and price precious metals such as gold, platinum, palladium, and silver. One troy ounce is equivalent to 31.1034768 grams, which is slightly heavier than a standard ounce that has 28 grams. The troy ounce is the only measure of the troy weighting system that is still used in modern times. When prices of precious metals are listed per-ounce, it is often referencing the troy ounce. The troy weight system has been replaced by the carat system in the world of precious gems and stones.

In summary, a troy ounce of silver is a unit of measurement used to weigh and price silver, and it is equivalent to 31.1034768 grams.