On November 2019 I went back to Venezuela, and the biggest shock for me was that people started trading goods using US Dollars. This isn't "legal", but it has become so common that I hardly ever had to have the official currency "Bolivar" with me during the three week period that I was there. I was told that trading using US Dollars became mainstream during the blackout period on which you had no access to any electronic means to pay and given that Bolivares in cash were scarce, people began using US Dollars as currency. Al tough both are accepted.
Anyway the problem goes much much deeper. But I wanted to know how is this called and if any other country has ever gone through a process similar to this one before?