BitCoin, as explained to my 5 year old
me: You have piggy bank?
kid: Yes papa!
me: how would you feel if i steal from it?
kid: very very sad. then i cant buy hoverboard on my birthday
me: what if you can hide that piggy bank in whole wide world, like some part of it in America, some in Africa, some in Europe and India?
kid: than i have to make a very big robot with very long hands to open it
me: well that’s BitCoin! we take all money and put in so many small piggy banks around the world and you can take out money only when you can take it out from all of them at same time!
me: so no one can steal your money?
kid: only when you can make a big big robot! and for that you need lots of money!