What is a “fiat” currency? Are there other types of currency?
"A ""fiat"" currency is non-convertible paper currency that a government establishes as legal tender. Most countries today are using fiat currencies. The rest have currencies pegged (or convertible to) US Dollars (which is a fiat currency). In the past, money was usually based on precious metals such as gold or silver. Until the end of the gold standard, you could theoretically go the the US Treasury with a US Note or Federal Reserve Note and convert the note into a fixed quantity of gold or silver (depending on the note). The US had a bi-metallic currency policy for political reasons, which means that money was backed by both gold and silver." In short. A fiat currency is money that has value only because (usually) a government says it does.  A counter example (non-fiat currency) is a gold coin that has intrinsic value usually because it is made of valuable materials that people would trade goods/services. That is the value comes from what you are holding more than what it represents. "fiat in Latin means ""let it be"" or ""let it happen"" - as in ""fiat lux!"" meaning ""let there be light!"". Thus, fiat money means money that are created by the government decree - they would be random worthless pieces of paper otherwise, so the government says ""let this paper be worth $100"" and it becomes $100. Non-fiat money have some value that is beyond declaration - e.g., gold coin has the value of gold that is made of. Since 1971, almost all world currencies are fiat money." There's two types of categories at play that define currency types - but I think the first is more like what you are after.  The first is there are essentially three currency types now recognised - see them described here: http://finance.mapsofworld.com/money/types/ The second is currencies can be categorised by the type of economy from which they are generated (reserve/commodity/etc) - see them described here: http://www.forextraders.com/learn-forex-trading-course/major-currency-pairs.html
What? Our currency isn't backed by debt currently. It's a fiat currency. Now, if you're asking whether we could back the value of our currency against some type of debt, sure we could, but it would be an incredibly poor decision.   The Constitution doesn't specify the type of currency the U.S. has. It gives Congress that power to either delegate that decision, as in the case of the Federal Reserve or pass their own laws. "It's very hard to measure the worth of an abstract concept like money, particularly over long periods of time. In the modern era we have things like the Consumer Price Index (CPI) in the United States, where the Bureau of Labor Statistics literally sends ""shoppers"" out to find prices of things and surveys people to find out what they buy. This results in a variety of ""indexes"" which variously get reported by media outlets as ""inflation"" (or ""deflation"" if the change in value goes the other way). There are also other measurements available like the MIT Billion Prices Project which attempt to make their own reading of the ""worth"" of currencies. Those kinds of things are about the only ways to measure a currency's change in ""value to itself"" because a currency is basically only worth what one can buy with it. While it isn't ""all the world's currencies combined"", there is a concept of the International Monetary Fund's ""Special Drawing Rights (SDR)"", which is a basket of five currencies used by world central banks to help ""back"" each other's currencies, and is (very) occasionally used as a unit of currency for international contracts. One might be able to compare the price of one currency to that of the SDR, or even to any other weighted average of world currencies that one wanted, but I don't think it's done nearly as often as comparing currencies to the basket of goods one can buy to find ""inflation"". Even though one might think what would be important to measure would be overall Money Supply Inflation, much more often people care more about measuring Price Inflation. (Occasionally people worry about Wage Inflation, but generally that's considered a result of high Price Inflation.) In order to try to keep this on topic as a ""personal finance"" thing rather than an ""economics"" thing, I guess the question is: Why do you want to know? If you have some assets in a particular currency, you probably care most about what you'll be able to buy with them in the future when you want or need to spend them. In that sense, it's inflation that you're likely caring about the most. If you're trying to figure out which currency to keep your assets in, it largely depends on what currency your future expenses are likely to be in, though I can imagine that one might want to move out of a particular currency if there's a lot of political instability that you're expecting to lead to high inflation in a currency for a time." The IRS defines income quite specifically. On the topic What is Taxable and Nontaxable Income, they note: You can receive income in the form of money, property, or services. This section discusses many kinds of income that are taxable or nontaxable. It includes discussions on employee wages and fringe benefits, and income from bartering, partnerships, S corporations, and royalties.  Bartering, or giving someone wages (or similar) in something other than currency (or some other specifically defined things, like fringe benefits), is taxed at fair market value: Bartering Bartering is an exchange of property or services. You must include in your income, at the time received, the fair market value of property or services you receive in bartering. For additional information, Refer to Tax Topic 420 - Bartering Income and Barter Exchanges. Bartering is more specifically covered in Topic 420 - Bartering Income: You must include in gross income in the year of receipt the fair market value of goods or services received from bartering. Generally, you report this income on Form 1040, Schedule C (PDF), Profit or Loss from Business (Sole Proprietorship), or Form 1040, Schedule C-EZ (PDF), Net Profit from Business (Sole Proprietorship). If you failed to report this income, correct your return by filing a Form 1040X (PDF), Amended U.S. Individual Income Tax Return. Refer to Topic 308 for information on filing an amended return. More details about income in general beyond the above articles is available in Publication 525, Taxable and Nontaxable Income.  It goes into great detail about different kinds of income. In your example, you'd have to calculate the fair market value of an avocado, and then determine how much cash-equivalent you were paid in.  The IRS wouldn't necessarily tell you what that value was; you'd calculate it based on something you feel you could justify to them afterwards.  The way I'd do it would be to write down the price of avocados at each pay period, and apply a dollar-cost-averaging type method to determine the total pay's fair value.   While the avocado example is of course largely absurd, the advent of bitcoins has made this much more relevant.  Publication 525 has this to say about virtual currency: Virtual Currency.   If your employer gives you virtual currency (such as Bitcoin) as payment for your services, you must include the fair market value of the currency in your income. The fair market value of virtual currency (such as Bitcoin) paid as wages is subject to federal income tax withholding, Federal Insurance Contribution Act (FICA) tax, and Federal Unemployment Tax Act (FUTA) tax and must be reported on Form W-2, Wage and Tax Statement. Gold would be fundamentally similar - although I am not sure it's legal to pay someone in gold; assuming it were, though, its fair market value would be again the definition of income.  Similarly, if you're paid in another country's currency, the US dollar equivalent of that is what you'll pay taxes on, at the fair market value of that currency in US dollars. They can only do that because Coinbase interfaces with fiat currency. As more transactions and holding become denominated in crypto, it will be more difficult for them to tax (if you are using an unlinkable crypto). If I pay someone with Monero or most coins, then the government won't know who was involved in the transaction. Gold is money. If fiat money fails, only physical assets will count. Gold has been an historic store of wealth. Silver is also historically a good thing to possess when governmental systems fail. Don't buy paper gold, it is based on illusion. No one knows what will happen this time, but fiat money will likely fail again, as it has many times. Good luck to you for at least trying to prepare, you are an inspiriation. "Currencies that are pegged or fixed require that foreign currencies are held by the central issuer at a proportional amount. This is analogous to having a portfolio of currencies that the central bank issues shares from - in the form of its own currency. We will continue with this analogy, if the central bank says these ""shares"" are worth $1, but the underlying components of the portfolio are worth $0.80 and decreasing, then it is expensive for the central bank to maintain its peg, and eventually they will have to disregard the peg as people start questioning the central bank's solvency. (People will know the $1 they hold is not really worth what the central bank says it is, because of the price changes people experience in buying goods and services, especially when it comes to imports. Shadow economies will also trade using a currency more reflective of labor, which happens no matter what the government's punishments are for doing so). Swiss National Bank (central bank) did this in early 2015, as it experienced volatility in the Euro which it had previously been trying to keep it's currency pegged to. It became too expensive for it to keep this peg on its own. The central bank can devalue its currency by adjusting the proportions of the reserve, such as selling a lot of foreign currency X, buying more of currency Y. They can and do take losses doing this. (Swiss National Bank is maintaining a large loss) They can also flood their economy with more of their currency, diluting the value of each individual 1 dollar equivalent. This is done by issuing bonds or monetizing goods and services from the private sector in exchange for bonds. People colloquially call this ""printing money"" but it is a misnomer in this day and age where printers are not relevant tools. The good and service goes onto the central bank's balance book, and the company/entity that provided the service now has a bond on its book which can be immediately sold to someone else for cash (another reading is that the bond is as good as cash). The bond didn't previously exist until the central bank said it did, and central banks can infinitely exchange goods and services for bonds. Bond monetization (also called Quantitative Easing) is practiced by the Federal Reserve in the United States, Bank of Japan, European Central Bank and now the Central Bank of the Republic of China" If I hold a bond then I have a debt asset. If I hold physical silver then I have a commodity asset. If I hold the stock of an individual company then I have an equity asset. Equities, commodities and debts are the three kinds of assets that a person can hold.  Edit: I forgot one other kind of asset; monetary asset. If I stuff my mattress with cash (USD) I am holding a monetary asset.  Short-term Treasury Bills really behave more like a monetary asset than a bond. So besides actual, physical, currency I would categorize T-bill as a monetary asset.  https://www.treasurydirect.gov/indiv/products/prod_tbills_glance.htm "you want more information on what? The general bond market? This article is getting at something different, but the first several pages are general background info on the corporate bond market.  http://home.business.utah.edu/hank.bessembinder/publications/transparencyandbondmarket.pdf  If you are trying to relate somehow the issue of federal debt ( a la treasuries) to corporate debt you will find that you are jumping to a lot of conclusions.   Debt is not exactly currency, only the promise of repayment at a certain date in the future. The only reason that U.S. treasuries ( and those of certain other highly rated countries ) is interchangeable is because they are both very liquid and have very low risk.   There is very little similarity to this in the corporate bond market. Companies are no where near to the risk level of a government (for one they can't print their own money) and when a corporation goes bankrupt it's bondholder are usually s.o.l (recovery rates hover at around 50% of the notional debt amount). This is why investors demand a premium to hold corporate debt. Now consider even the best of companies, (take IBM ) the spread between the interest the government must pay on a treasury bond and that which IBM must pay on a similar bond is still relatively large.   But beyond that you run into a liquidity issue. Currency only works because it is highly liquid. If you take the article about Greece you posted above, you can see the problem generated by lack of liquidity. People have to both have currency and be willing to accept currency for trade to occur. Corporate bond are notoriously illiquid because people are unwilling to take on the risk involved with holding the debt (there are other reasons, but I'm abstracting from them). This is the other reason treasuries can be used as ""currency"" there is always someone willing to take your treasury in trade (for the most part because there is almost zero risk involved). You would always be much more willing to hold a treasury than an equivalent IBM bond.   Now take that idea down to a smaller level. Who would want to buy the bonds issued by the mom and pop down the street? Even if someone did buy them who would in turn take these bonds in trade? Practically speaking: no one would. They have no way to identify the riskiness of the bond and have no assurance that there would be anyone willing to trade for it in the future.   If you read the whole post by the redditor from your first link this is precisely why government backed currency came about, and why the scenario that I think you are positing is very unlikely."