Gold prices change throughout the business day, to the extent that the spot price must be updated every couple of seconds. This is because each trade of bullion that is made affects the average price, so during trading hours, the price is always in flux.
Spot prices are normally quoted as the price in U.S. dollars (USD) per troy ounce of .999 fine gold. Some sites also use the price per gram to allow easy worldwide price comparisons. The price listed does not take into account dealer or distributor markups or markups by the minting or manufacturing company. These can also change at any stage during the trading day, affecting the retail price of gold.