That part of the money in circulation not backed by gold is known as?

The part of the money in circulation that is not backed by gold is called "fiduciary issue." Fiduciary issue refers to the currency or money that a government or central bank issues without having the equivalent amount of gold reserves to back it up. In other words, fiduciary issue money is not backed by any tangible asset like gold, but it is based on the trust and confidence that people have in the issuing authority. This type of money is usually in the form of banknotes and coins that are widely accepted as a means of payment and a store of value. Governments and central banks can increase the amount of fiduciary money in circulation by printing more banknotes or minting more coins. However, too much fiduciary money in circulation can lead to inflation as it reduces the value of each individual unit of currency.