Paper money can fall under this just as easily. Even as a physical object its pretty worthless. Gold and Silver on the otherhand have a universal understanding of having "value" though, even if it's worthless without a stable economy. Your money, paper or not paper is fiat and its one of the worst scams in history.
I didn't know how to phrase it, but I know that UK currency is technically based on the gold in the Bank of England.
My £5 note is actually a promise from the bank that they owe me £5 worth of gold. When I trade my £5 note for an item I am technically trading them the banks promise of gold to that value.
In that sense my banknotes and coins technically have a physical object of worth behind them.
But as Otis said, worth of anything is arbitrary.
I just find it interesting that unlike most other things of worth, there is no physical aspect to cryptocurrencies at all. Ultimately I can hoard gold, or cash, or oil, or food, but I'll never store cryptocurrency in a vault.
That's not bad at all, it's just interesting to me that it exists. I understand its uses however.
