Most people know Bitcoin exists because of blockchain. But what is blockchain? It is an append-only database that consists of blocks that are linked by hashing. Here, each block contains many transactions of transferring value (but could be other things) between participants secured by cryptography; a consensus between many nodes that hold an identical database decides on which new block is to be appended next.
You don't have to understand the definition at this point; those are a lot of words to chew on! First, I'll explain blockchain to you so that you can adjust to this new knowledge as we move through this book.
Going back to the definition of blockchain, we can summarize the definition as an append-only database. Once you put something into the database, it cannot be changed; there is no Undo. We'll talk about the ramifications of this...
