Dollar Billionaire
This presumably refers to a person who has wealth equivalent to a billion U.S. dollars (as opposed to a billion units of some other currency).
I went looking for some validation of this, but I didn’t find any explicit definitions. What I did find were a lot of contextual quotes indicating this was the correct definition.
When anyone around the world speaks of a “billionaire,” you should technically ask “a billion of what currency?,” though it’s likely commonly accepted to mean “dollar billionaire” when used in English.
Why I Looked It Up
I heard the word at a conference in London. A Russian speaker said something like:
He became a billionaire… a dollar billionaire.
It had never occurred to me that someone might claim to be a billionaire but really just have a billion units of some other currency. While they wouldn’t technically be lying, they couldn’t be considered a “billionaire” in the colloquial sense.
I set out to find the cheapest currency in the world, in which you could technically claim billionaire status. As of this writing it’s the Iranian Rial – you could be an Iranian billionaire (a “rial billionaire”) and only have about $24,000 U.S. dollars.