It’s said that you could ask a physics PhD candidate to answer the question “Why is the sky blue” and that would be a adequate method to screen PhD candidates. Same statement for an Economics PhD candidate - but you would ask “Define money”.
Ultimately it seems money is whatever gains the confidence of a critical mass of people and is relatively easy to transfer back and forth.
Bitcoin isn’t “backed” by anything but then again neither is the almighty dollar. I predict that this will never gain the stature of, say, the dollar, but in the end who really knows?