Fiat currencies are simply an idea. They portray the idea of an asset that governments and Central Banks have impressed on societies to believe as good value. In reality, Fiat currencies have zero intrinsic value other than the piece of paper or metal coins they are made of.
Money is whatever any given socio economic environment accepts as a medium of exchange and store of value. From antique barter economies to the modern digital age money has taken multiple forms from seashells to gold, other precious metals, paper and most recently cryptocurrencies.
Different forms of money have been adopted over time with different sets of properties and tradeoffs. As we have progressed from ancient barter economies to the present day, money forms have evolved and adapted to suit the requirements and the prevailing needs of their time.
What this article shows is that all available money forms used throughout history are far from perfect and present various weaknesses.
Money is a language, a way of expressing value to carry out exchanges of goods and services between human beings. It is a belief, a technology developed to be able to exchange and store value over time.