What Is a Double-Spend?

Before we go further, let's talk about double-spending. Double-spending is when someone tries to spend the same Bitcoin more than once. It's like making a copy of a digital file and sending it to multiple people. In a regular currency system, like using cash, this isn't possible because there are rules and a central authority (central banks) that keeps track of everything. But with digital currencies like Bitcoin, we need a way to prevent double-spending.

That's where the blockchain comes in. The blockchain keeps a record of all the transactions, and everyone has a copy of it. So, if someone tries to spend the same Bitcoin twice, everyone will see it and know it's not valid.