Digital money recorded on a public ledger rather than issued by a bank. Transfers cannot be reversed and there is nobody to appeal to, which is why scams favor it.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
cash handed over in a room with no doorman.
For example
You send it to the wrong person by mistake. There is no bank to call and nobody to reverse it. It has simply gone.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.