If you look at the asset portion of the block explorer you can click on any asset and then click the info tab. This will explain more about the asset. See: https://bitsharesblocks.com/assets/market
. Precious metals are nearly always measured in Troy Ounces, sometimes abbreviated ozt.
There are other assets, like Oil, that are pegged to the barrel. Confusingly, "GAS" is 1 gallon (US) of 87 Octane. I would expect "GAS" to be natural gas and "GAS" here to be something else like "GAS-87" or "PETROL-87" and what about gasoline by the liter anyway? But, I digress.