The Value of Money
You define it. Society doesn't.
In the old days, Viking kings would make money based on the goods they had seized during raids… As in melting gold and silver. The money had value because it was based on actual wealth.
In modern society, however, money is an illusion. Printed paper. With nothing to back it up. World monetary systems, especially the U.S. dollar, only exist because of blind faith, overall stupidity, and the masses taking part in the game.