A blockchain is a distributed database, meaning that the storage devices for the database are not all connected to a common processor. It maintains a growing list of ordered records, called blocks. Each block has a timestamp and a link to a previous block.
Cryptography ensures that users can only edit the parts of the blockchain that they “own” by possessing the private keys necessary to write to the file. It also ensures that everyone’s copy of the distributed blockchain is kept in synch.
Imagine a digital medical record: each entry is a block.
Read more at Forbes