Money is the Representation of Productive Work
Gold is not money.

Paper is not money.

What is money?

What a thing is is defined by its fundamental essence which identifies its being, its nature.  A thing has many characteristics however there is only one essential characteristic that defines it. What then defines the nature of money?

Money is productive work first. Then this action is represented by a thing, the object agreed upon as the symbol to represent the action.

The word money, the concept, then is initially conceived from these percepts of the action of people performing productive work and not from the thing itself, not from the thing chosen as the symbol of having performed productive work. The medium of exchange is only necessary because productive work has been performed. To understand the concept of what money is, then, we must deduce its meaning back to its most irreducible primary which is to the cause, the first principle, as to why the symbol became necessary at all. Knowing the cause of a thing or action is to know the thing or action. We say a thing is such and such because, and then proceed to identify the cause. Money is used as a medium of exchange because it was introduced as a means of equalizing the measure of disproportionate productive work. Thus, money is because of productive work. The work always yields a final product so to say that money equalizes the price of products that are not commensurate is very close to a formal definition but does not identify its one essential characteristic; for it is the work that creates the product so essentially the money is measuring the value of the production and not just the product.

For example, observe a transaction between a builder and a shoemaker. The builder needs shoes and the shoemaker needs a house but the builder wouldn't trade a house for a pair of shoes nor would he accept 1,000 pairs of shoes for a house. So money was conceived as a measure for the exchange among producers whose labor is valued more and those whose labor is valued less. This conception is then objectified by an agreed upon perceptual unit; a real thing that can represent the conception of money. Say that one monetary unit will equal 1 pair of shoes. Now the builder can give the shoemaker a unit for a pair of shoes. The shoemaker can sell a thousand pairs of shoes and then give the builder 1,000 units for a house. So money actually represents an exchange between producers who trade their work for the work of another. Also, the agreed upon unit of measure has a certain long term durability and stability associated with it so that it can be held and used in an exchange sometime in the future with the same or similarly expected results as if it were exchanged presently.

What I have just described is not a theory. It is precisely why humans invented money. It is the starting point from which we learn what money is and enables us to integrate the concept of money into our knowledge.

Now introduce another participant to the exchange in the example above but this party does no work and offers you no product but nevertheless demands that you give him your product. If such a party were to attempt to barter his nothing for your something you would undoubtedly walk away. You would walk away unless you were forced or coerced to accept the exchange of nothing for something. This participant in the transaction then would not be a trader exchanging for mutual benefit; instead, the participant is a robber offering you nothing but taking your something. Force is the mediator of the exchange.

Now assume the third party does not introduce force to the transaction but instead deception. He gives to you what appears to be the same agreed upon unit that measures the exchange of work. Your presumption of course is that that party must have earned those units by working too. However, you have been duped. Instead of working to earn units of money, this person has debased or falsified the unit. So the dishonest party has done zero productive work and represented himself as if he did. He passes off the deception of having worked, the imitation of work, the impersonation of work. The corrupted party is passing you counterfeit. The corrupted party is a thief. Deception is the mediator of the exchange.

It is important to see that both events of robbery and theft require compulsion. The exchange is no longer represented by money since the full value on both sides of the exchange of trading 100% of something for 100% of something is gone. By robbery, the exchange is always 0% value for 100% full value. By theft, the exchange is usually a fraction of full value for 100% full value but can also be an exchange of 0% value for 100% value.  Since robbery represents the act of force then the robber always steals full value. Since theft represents the act of deception then the thief will attempt to steal the largest amount of value that they can. By identifying whether money or counterfeit is used to mediate the value exchanged, then we can conclude that a banking system that facilitates the exchange of full value is honest and that a banking system that facilitates the exchange of fractional value is dishonest. The former manages a monetary system and the latter manages a counterfeiting system.
What modern economics calls the banks' multiplier effect or leverage and the instant conjuring of currency written as a debt against the customers account is not the production of money but instead the creation of counterfeit. That is it is not the representation of the measure of work already performed. Instead it is the impersonation of work performed. It took no productive work to create the leverage of  the multiplier or the instantaneous magical blip dishonestly placed on the books of account. All it took was an ink blot or an enter key. It represents no productive work and is therefore not money but instead it is counterfeit. Money is the measure of work a person does to produce their product which satisfies the voluntary demand for value of others who likewise do the same. Counterfeit is the impersonation of productive work done when actually none has been performed and the demand it satisfies therefore must be involuntary.  The purpose of counterfeit then is to represent the illusion of trading something for something when in fact it is the trading of nothing for something. Whomever trades nothing for something is a thief. Therefore, just as we can identify that money is because of productive work, we can identify that counterfeit is because of no productive work.

It is this exchange of counterfeit that lowers the producer's power to purchase. Whomever receives the counterfeit first trades it for the products of other people's work. This is theft, not investment. As the counterfeit is passed along its power to purchase decreases and what one would have purchased with the higher power to purchase before the counterfeit was introduced has been stolen from them. The repeated process of introducing more and more counterfeit into the economy necessarily then represents the increasing theft of the purchasing power from those who do productive work by those who do not. Counterfeiting therefore is the primary cause of the atrophy of the middle classes as they are surreptitiously pummeled into submission. Such is the dishonest nature of the fractional reserve counterfeiting systems and how well established thieves steal from producers as the means of sustaining their usurped livelihoods.

The modern definition of money that defines money as a medium of exchange is wrong. That it is a medium of exchange is a characteristic of money but it is not the essence of what money is. It is not money's nature since it indicates nothing of its cause. What we choose to describe something as does not define what it is. A thing is what it is first and then defined correctly in accord with that fact. Just as money can mediate an exchange, so too can counterfeit. Therefore, since this is a characteristic of each of them then a more precise defining characteristic must be identified for both of them separately. Money is the representation of productive work, counterfeit is the representation of stealing from productive work. To understand what money is, we do not weigh the medium or hold it under ultra-violet light, we examine not the media stuck in the middle of the exchange. Instead, we identify what is on both sides of the exchange and ask, "Regardless of the media stuck in the middle, is value for value being exchanged or is it the imitation of value for value? Modern thieves depend upon their victims to not understand the difference between money and counterfeit. They depend on their victims' preoccupation with the perception of the units themselves and not the conception of why the units became necessary at all and how that necessity determines which units originate as money and which units originate as counterfeit.  The thieves count on their victims not knowing that money was conceived to satisfy the need for people to exchange the products of their disproportionate work. The unit of measure was then introduced as the means to equalize the disproportion.

Having this knowledge is understanding money simpliciter and counterfeit simpliciter and its application to all that follows it then lifts the veil of deception from the monopoly of fractional reserve counterfeiting.

(The classic definition of money as I have described here is my paraphrase of Aristotle's discussion in his Nicomachean Ethics; Book V, section 5, paragraph 3.   Aristotle never identified the concept of counterfeit but nevertheless I have reasoned it from this passage. I then apply these two opposite concepts, money and counterfeit, to economics while never contradicting the origin of each concept. The origin of each concept is identified by how  individuals meet their demands for living as the means of their pursuit of happiness.)