when speaking to your grandparents please do not let this be the first sentance out of your lips
"bitcoin is a decentralized, digital money. that is created, held and spent electronically around the world"
it will raise more questions than answers.
try keeping it simple, you dont need to explain all the details using bigwords
its money on used from the computer that is secured by you and not a bank, so theres less fee's and less deays. its money without limits grandma
Second this. That line and similar, have been used to describe bitcoin longer than bitcoins been a thing.
Though it's a nice, tidy summary of what it is, it's not necessary for everyone to know it off heart.
If someone approaches you and asks about bitcoin rather than googling it,
replying with "Bitcoin is a peer-to-peer, decentralised, digital currency"
will give you the pleasure of watching their eyes glaze over and their face display the purest expression of regret.
It's not the hardest thing in the world to understand. We all know how to get to the moon. Very few of us know how to build a rocket.