Money is the lifeblood of the economy.
You can't buy and sell stuff without money. The Federal Reserve has established three different money supply classifications. These are known as M1, M2, and M3. M1, in essence, is the sum of all the currency in circulation plus the total of everybody's checking accounts. Now, it only makes sense that there should be a strong relationship between the amount of money folks have and the amount of money that winds up getting spent.