Hi David and Peter, my own definition of a digital currency is much like Peter's, or maybe broader, any electronic account, that is serving at one of the functions of money (unit of account, store of value, medium of exchange or standard of value which was emphasized by Jevons and Keynes particularly relevant for international comparisons). So the public has had digital money since at least online banking and even before that with credit cards tied to electronic accounts, but perhaps if we limit our subject group to consumers we could call that plastic money. I would call it e-money.
Central Bank digital currencies is an interesting new and potentially radical departure from our current system, or it might simply look identical to the consumer as our current system. The more radical version would have us have our account at the central bank.
This later version dis-intermediates banks, and removes their power to create money. It could potentially unite fiscal and monetary policy into one category, similar to the way that MMT (Modern Monetary theory) describes their theory of money.
It would be interesting to hear your opinions. As a public good it could reduce transaction costs and even apply a veil of confidentiality if it was blockchain based or if you trusted your central banker to do that. I'm sure it would be a permissioned blockchain. I believe that Cambodia already has (or had) a blockchain sovereign central bank currency.
It is great solution for many government policies, especially in developing countries, as it solves their current inability to tax, it can make immediate and real time payments to anyone or everyone (like Biden's Corona Virus rescue payments), it could include claw backs for all those companies that cheat on their information, and monetary policy could be direct to main street and not wall street which is currently a stimulus for excessive speculation.
Obviously there are downsides but I leave others to list those.