- It's backed by nothing.
- It's not a fair medium of exchange because it physically cannot circulate very far from 'money printers' (not many hops) before it's taxed down to nothing. This means that it's unevenly scarce based on social proximity; unfair by design. Cantillon effects on steroids.
- It doesn't even exist as a single cohesive concept; the US dollar in your bank account is not the same as the US dollar in your friend's bank account and it's not the same as the US dollar which European traders use to buy derivatives (e.g. Eurodollars)... There are literally thousands of different ledgers (banks, institutions, in different countries), each presenting its own interface supposedly showing their holdings of this mythical unit called 'The US dollar' which is actually thousands of different currencies, which happen to share the same name, scattered around the world and held together only by regulators whose only shared interest is to print more units for themselves than the next guy does. Slow and fallible human regulators represent the only layer of 'consensus' which exists for the entire fiat monetary system; they move at snails' pace in a world of high frequency trading.
Money is never backed by nothing, or it's worthless. It may not be backed by anything physical, but it's always backed by some form of trust. National currencies are backed by trust in the corresponding government and institutions.
I have a phd in economics. Most researchers in that field have never even heard of any of those tools. Maybe LaTeX, but few actually use it. I was one of very few people in my department using Zotero to manage my bibliography, most did that manually.