It is not straightforward to define what “money” is in a modern national economy. Simply tallying the amount of coins and paper currency is inadequate. Most buying and selling is now done by shifting numbers between abstract bank accounts, not by pushing a bundle of bills across a table. Thus, these bank accounts serve the functions of money (medium of exchange and store of value). The question then arises as to which of these financial accounts to regard as money.
Among financial assets, there is a broad spectrum of liquidity. Typically you can write a check on your checking account which, when it clears, provides immediate and final settlement for a purchase. On the other hand, if you want to tap your brokerage account with its holdings of Apple stock to buy a television, you would typically have to sell (liquidate) your stock. A third party would have to be willing to give you something more money-like (e.g. credit your money market fund at your brokerage) in exchange for the stock at some negotiated price. Then you might have to transfer the funds from your brokerage fund into your bank checking account before you can actually buy that TV. Because of all these intermediate steps, and the fluctuating value of the stock before you complete the sale, the stock holding would not be counted as “money”, even though its value enabled you to ultimately make your purchase.
There are a number of measures of money in modern economies. In the U.S. some of these are:
M0: The total of all physical currency (coins and paper bills).
MB (“Monetary Base”): The total of all physical currency (coins and bill) plus Federal Reserve Deposits (special deposits that only banks can have at the Fed). This is money essentially created by the government plus the Federal Reserve, which does not necessarily enter the private economy to be spent.
M1: Physical currency circulating outside of the Fed and private banking system, plus the amount of demand deposits, travelers’ checks and other checkable deposits. This is highly “liquid” money, i.e. accepted and used for transactions in the private economy.
M2: M1 + most savings accounts, money market accounts, retail money market mutual funds, and small denomination time deposits (certificates of deposit of under $100,000). The funds in these additional savings and money market accounts can in general be easily transferred to checkable accounts, and thus could go towards making purchases if desired.
MZM: “Money Zero Maturity” is one of the most popular aggregates in use by the Fed because its velocity has historically been the most accurate predictor of inflation. It is M2 – time deposits + institutional money market funds.
Below is a chart showing the growth in the U.S. in the past fifteen years of M0 (total currency, labeled “currency in circulation), MB, M1, and M2. The grayed areas are recessions, i.e. 2008-2009 and the present. 
The M1 money supply (green line) was about $1.4 trillion ( $1,400 billion on the chart) in 2005, was fairly steady for several years, then started a steady ramp up to $4 trillion by January, 2020. Due to the extraordinary events associated with the Covid-19 shutdown (government stimulus package plus Fed purchases of securities), M1 jumped up to $ 5.4 trillion by August of this year. M2 followed similar trends, though on a much larger scale, rising to$18.3 trillion this year. This compares to a current U. S. total GDP of about $21 trillion.
The lowest line on the chart is the physical currency (blue line), which has grown slowly but steadily. The “Total MB” (red) line, was essentially on top of the blue line up until the 2008-2009 recession. Since MB = physical currency plus reserves, this meant that the amount of money in the reserve balances at the Fed of the private banks was nearly zero before 2008. The reserves jumped up (difference between the red and blue lines) in 2009, with the onset of massive purchases of securities by the Fed (“quantitative easing”). The Fed buys these securities from the banks, and credits their reserve accounts. The Fed has tried to taper down its holdings in recent years (red line declining 2015-2019), but suddenly purchased trillions more this spring (red line jumping up in 2020). Most pundits hold that all this Fed money injected into the financial system has been the major cause of the enormous rise in stock prices in the past decade, especially in the past six months.
 Chart produced on the St. Louis Fed “FRED” site, https://fred.stlouisfed.org/categories/24 . This site has a wealth of economic data. Unfortunately, it is not easy to change units, so I was stuck with “billions” instead of “trillions” for the axis labels. Also, the M0 and MB numbers were only available in “millions”, so I had to divide those numbers by 1000 to get them to fit on the plot with M1 and M2. The grayed out spots on the graph labels is where I blotted out the “ /1000 ” which the plotting software put in. It would have been cleaner, in retrospect, to have exported the data to Excel and replotted it there.
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