'Seigniorage'

Seigniorage is the difference between the value of currency/money and the cost of producing it. It is essentially the profit earned by the government by printing currency.

It can also be termed as a source of revenue for governments as the value of money printed is generally higher than the cost of producing it. As obvious, if the currency produced values more than the cost involved in its production, the government earns a profit. If the cost involved in its production crosses its value, then the government suffers a loss