Digital Money is the inscription of value on a public ledger. Digital money is the self-custody of value where legacy banking does not support this notion. Bitcoin was the first widely available digital currency; nowadays there are many more coins, tokens, digital assets and real-world assets available on technology built on the back of Bitcoin.
Decentralized Finance is a natural extension of digital money which democratizes access to financial tools. The simplest tool of DeFi is trustless lending + borrowing.
I write about digital money often here: