gold standard
1. Literally, a monetary standard where a currency's value is defined by an existing and fixed amount of gold. There are many who believe that the country should return to the gold standard for a more secure means of issuing currency.
2. By extension, a well-established and widely accepted model or paradigm of excellence by which similar things are judged or measured. Her research methodology in the late 1960s has since become the gold standard for drug trials today.