gold standard 
noun
1The system, abandoned in the Depression of the 1930s, by which the value of a currency was defined in terms of gold, for which the currency could be exchanged.The classic gold standard was a monetary regime constructed to preserve financial and economic stability....
- National currencies based on the gold standard were thought to be uniform, leading toward a global monetary standard.
- The British thereby laid the basis for what was to become the world monetary system based on the gold standard and bank notes.
1.1A thing of superior quality which serves as a point of reference against which other things of its type may be compared: breast milk provides the gold standard by which infant feeds are measured...
- This type of process may then be used as best practice, serving as a gold standard to be implemented in other facilities.
- Once upon a time, Disney provided the gold standard in family entertainment, from animated fairytales to Mary Poppins.
- Despite their intriguing objectivity and precision, billing records do not provide a gold standard.