hard currency

nouns

a currency that is not likely to depreciate suddenly in value
"the countries agreed to conduct their bilateral trade in hard currency, replacing previous barter arrangements"; "Germany once had a solid economy, good fiscal and monetary policies, and a hard currency"
is a type of (narrower)
the metal or paper medium of exchange that is presently used
money in the form of bills or coins
"there is a desperate shortage of hard cash"