The Gold standard is the practice of Governments to fix their currency to the price of Gold, and to offer to exchange their currency for an equivalent amount of it.
For example, if the price of the currency was set at $100 per ounce of gold, then $1 would be worth and exchanged for 1/100th of an oz. of gold.
Other commodities or a basket of commodities could also be used to set the price of the currency.
The United States officially went off the Gold Standard in 1971.