The four strangers in this example represent Bitcoin’s community of users. We are using strangers to explain this, because in the real world, most Bitcoin users do not know each other. The notebooks in this example represent what's called the Bitcoin Blockchain. The Blockchain stores a public record of every single bitcoin transaction ever made. The Blockchain is not on paper but 100% digital and public.



Most importantly, there are thousands and thousands of identical copies of the Blockchain held by users around the world. All these copies are kept in sync by the system that runs the Blockchain.