People have used salt, seashells, cigarettes etc as money. Because money is what we call the good or tool that is used as "money".

The is used to store value. To exchange for other goods. As a unit of account.

A goods or tool becomes money when it is used as money.

In a prison cigarettes becomes money when that is the goods used for money.

Different goods or tools can be better or worse money depending on the qualities it has.

There is no requirement that it has to be tangible or physical.

The requirements are that is has to do its job more or less. It has to work as a:

Store of value Means of exchange Unit of account

And to do so it has to be fungible, transportable and durable easy to verify, etc.

Bitcoin has all those properties and is designed to excel at all of them. Some say it does not store value, because it is too volatile, but bitcoin does not contain volatility, the volatility is caused by other humans. And volatility is not a problem as long as it has remained in value or increase in value between time A and time B the volatility in between does not matter at all. So far that requires could require that you hold it for more than 2-4 years but it will go down and become better and when it does it becomes even more valuable as more and more people see that it is here to stay and see that they can trust that it stores value and even increase in value.

So far it have and it seems like a given that it will continue to work and I would not bet against Bitcoin.

Gold is not bad, but today it does not work as a means of exchange for daily items and it probably can not as people will not go back from digital. Digital is superior at saving time and being verifiable.

https://www.thoughtco.com/what-is-money-1147763

