A gold gram is the amount of value represented by one gram of gold. It is a unit of account frequently used for digital gold currencies. It is sometimes denoted by the symbol "gg" or "AUG".
A milligram of gold is sometimes referred to as a mil. Therefore, 1000 mil = 1 AUG.
A possible source of confusion is that gold grams are often priced by the traditional Troy ounce. To simplify this mis-marriage of units, services such as BullionVault are increasingly using kilogram prices of gold. Kilogram gold prices are also commonly used by the Zurich Gold Pool.