First is this definition from L. Ron Hubbard:
Money is an idea backed by confidence
That's an interesting definition, because it tells you how come the Federal Reserve has been able to create money out of nothing for so long and yet it still has value. People have confidence in dollar bills so, despite the fact that the Fed has been printing (and I mean that in the electronic as well as the ink sense) money by the truck load, which under normal circumstances would make the money worth less and less until it became worthless, there are still plenty of people in the world who have confidence in the dollar.
That may or may not last. But it is the key to surviving this current crisis.
For more data on money and finances there are these courses you can take: