What Do You Get When You Buy a Gold Troy Ounce

So what do you get when you buy an ounce ?

The troy ounce is heavier than the typical grocery store (avoirdupois) ounce used in the USA.

When you purchase a 1 ounce silver or gold coin, you are receiving a "troy" ounce. If you put that same 1 troy oz. coin on a grocery store scale you will find that it weighs about 10% more than the food (avoirdupois) ounce you are familiar with. It will weigh about 1.1 avoirdupois ounces. A troy ounce is equivalent to about 31.1 grams

Separately, the troy weight system has it's own definition of a "troy" pound. A "troy pound" contains 12 troy ounces or 373.24 grams (which is over 13 avoirdupois ounces).
It is thought that the troy ounce was named after a weight system used in Troyes France during the Middle Ages.