I wouldn't tell much but will use simple words such as its a digital currency that can be use as payment for goods and services online whereas the seller is willing to receive bitcoin.
It has an unstable value that the market gives depending on the demand and supply of it. And if that isn't enough its better for him/her to watch tutorials that's explanation bitcoin with some visual graphics.
Definitely visuals! Infographics and other videos that covers the gist of crypto is good to start with
It's easier and more entertaining while learning if there are visual and infographics that can easily be picture out by the person you are explaining what bitcoin is. Explaining bitcoin in the simplest way can easily be done but once that person wants to dig deeper and learn more things about bitcoin.
I speak about such things only to those people whom I trust. I do not consider it necessary to tell everyone about this. If someone asks me what bitcoin is, I answer that there is a lot of information on the Internet
Before I was so careless that even the people I don't trust who just came by to ask me about it, I'm answering them but now I've changed.