Blockchain is a growing list of records, called blocks, that are linked using cryptography in a *linear sequence forming a chain. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data. By design, blockchain is resistant to any modification of the data.
Here is a link to a more elaborate article. We highly recommend you to give this one a read since it has broken down the most important aspect of blockchain which is the decentralised consensus to how would it look like, in a, “pre-tech Pen and Paper era, on an island”.