Why yes, I am making the title purposefully vague so that (hopefully) the thread can evolve without getting closed. To start out, though: mediums of exchange.
Description: Two humanoid figures are standing side by side. The right-side figure is holding a rock in its hand. Right side figure: Let's agree that this shiny rock is worth 2 sheep. Left side figure: Sounds fake but ok.
Here's my understanding of it. For any medium of exchange to work, there is a single basic requirement:
• Everybody involved has to agree on the value of the medium (whether it's shiny rocks, pieces of metal, pieces of paper, code in a computer, etc).
Everything else needed is needed because it supports this.
For instance, a limit on how many tokens are available. If the medium is shiny rocks, and all you have to do to get a shiny rock is go outside and pick one up... well, are you likely to exchange two sheep for a shiny rock? Even if that shiny rock would get you three goats? I mean. So would each of the million shiny rocks by the road on the way to the goatherd's place. "Nah," you say, "I think I'll keep my sheep and carry on making my own clothes from their wool, occasionally eating them, etc."—and Requirement One collapses.
Or a limit on value fluctuation: nobody wants to give up a whole rock for a cup of coffee only to discover that if they'd waited a day it would've bought them ten cups, nor to give up ten cups of coffee for a shiny rock when yesterday they would've gotten ten! This leads to arguments... and Requirement One collapses.
Money is the name we give a medium of exchange with widely agreed-upon value (like precious metals... or numbers in a computerized bank account).
Currency is what we call the things that are actually exchanged (like coins made of or representing precious metals... or numbers in a computerized bank account).
Fiat currency is things that are exchanged but aren't money (like coins neither made of nor representing precious metals, or numbers in a computer that aren't part of the financial system).
Forgeries are things that look like they're precious metals, or coins made of precious metals, or coins (or bills) representing precious metals, or numbers in a computerized bank account—but aren't.
And cryptocurrency....
Well, cryptocurrency is an attempted medium of exchange; it's supposed to be money.
To get your metaphorical hands on a piece of cryptocurrency, you can either buy a whole lot of expensive computer equipment (using standard currency) and pour electricity into it (paying for that with standard currency) until it solves a fancy computer problem and spits out your very own cryptocurrency token—or you can find someone who already has a token and give them something they'll agree to take for it (usually standard currency).
Now you have a piece of cryptocurrency! But what it's worth varies from person to person, location to location, day to day. There could be a better bargain across the street, or two years down the line, or even five minutes from now. In every exchange, the same question on both sides: "Have I been cheated?"
...And so Requirement One collapses.