How can I explain the meaning of Bitcoin to my grandma? I wrote a book about Bitcoin, and my proud grandma wanted to have a copy. So she got it, said "What a beautiful picture on the cover!" and - "What is this, Bitcoin?".

She doesn't know crypto-currencies, never used a computer. But she uses a PayPal account from her iPhone. How can I explain what makes Bitcoin special to a non-technical person? I don't mean introducing in using, and the existing question "What is Bitcoin?" with its answers is still much too technical.

Such challenges are not rare. I need to explain to my boss why I request some days off to go to a Bitcoin conference, and soon my daughter will want to know why daddy is so excited about his mining rig. My girlfriend needs to understand why I spend so much time researching Bitcoin.

Does anyone know eye-opening words? Perhaps an analogy or a metaphor would help? So grandma, girlfriend, daughter, boss - all may roughly understand and say "Ah, such a thing? Useful indeed!"
The one I use, at least for adults, is to make an analogy to a bank. When you write a check for some amount of money to another person and that person deposits the check, the bank does not physically take the amount of money and put it from your bin to another, they use a ledger to keep track of who has how much and they make sure the books balance. Bitcoin is essentially the same type of money in that there's a central ledger, but instead of only the bank having access to it, everyone has access to it. And much like signing over a check with your signature, you sign bitcoin transactions digitally.

As far as mining, the analogy there is that once a month or so, you get a bank statement that tells you your new balance along with all the transactions that happened on your account. If, for example, you overdrafted on your account, they'll tell you exactly what that cost and put fees on and so forth. As an aside, with bitcoin, you can't have a negative balance, so overdrafted transactions just simply don't go through. In any case, bitcoin creates a statement of not just your transactions, but everyone's transactions about every 10 minutes.

Usually, that's enough for people to understand what's going on. I avoid stuff like proof-of-work, mining reward, fixed money supply unless they're perceptive enough to ask those questions.