The root of money is a "promise to deliver value".
Money is a human construct.
Money originally was a form of bookkeeping to see who delivered on their promises (or who had outstanding undelivered promises). Sea shells worked in some locales.
Until recently, paper money was a receipt for gold or silver stored on one's behalf. That promise was reneged upon in 1933 (domestically) and 1971 (internationally). So today, paper money is a "note" with nothing of value behind it.
Where does the value derive? Contracts are denominated in dollars. Rent, salary, mortgage, contracts at the grocery store, etc. are all contracts denominated in dollars. That is where the value derives.
In small communities, money was a temporary placeholder for one's promises to deliver value. However, today, the world cannot track who delivers.
That is what "Promise Language" does. It is a standard format to describe transactions. The results can be stored on paper or in a computer so you know who delivers on their promises.
Theoretically, wealth translators replace the need for currencies. However, that is an expensive process, so currencies will always likely remain due to their economies of scale in reducing transaction costs.
What is money?
Anything of value that is agreed upon by both parties in a transaction.