What is the Blockchain?

Imagine a notebook where every Bitcoin transaction ever made is written down. Every 10 minutes or so, a new page (called a "block") is added.

Each page includes a special code (hash) that links it to the previous page. If you tried to change anything on an old page, the code wouldn't match anymore — everyone would notice immediately.

This notebook isn't stored in one place: thousands of computers around the world each hold a complete copy. That's what makes it nearly impossible to hack or cheat.