Block Chains

Blockchain was invented by Satoshi Nakamoto in 2008 to serve as the public transaction ledger of the cryptocurrency bitcoin. The invention of the blockchain for bitcoin made it the first digital currency to solve the double-spending problem without the need of a trusted authority or central server.

A blockchain is a growing list of records, called blocks, which are linked using cryptographic algorithms. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data to be resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way". Hence, a blockchain is generally managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without alteration of all subsequent blocks.

You can find a blockchain explanation into more detail here:

Mazonka, Oleg (29 December 2016). "Blockchain: Simple Explanation" (PDF). Journal of Reference http://jrxv.net/x/16/chain.pdf