Blockchain is a distributed ledger. In other words, it is a secure database used to store information. Blockchain is composed of data “blocks” linked together by cryptography “chains.” When a new block is created, it is tethered to the entire existing chain. This makes it very difficult to alter the data because a hacker would effectively need to update the entire chain. In a blockchain, data is shared across multiple devices (nodes) in a peer-to-peer network.
A user of the blockchain can opt to join the blockchain and have their own copy. The ultimate goal of blockchain is that information is shared, but not edited across the network.