Definition:
A blockchain is a continuously growing list of records, called blocks, which are linked and secured using cryptography. The first blockchain was conceptualised by a person known as Satoshi Nakamoto in 2008.
Each block typically contains a cryptographic hash of the previous block, a timestamp, and transaction data. A blockchain is a decentralised, distributed and public digital ledger that is used to record transactions across many computers so that the record cannot be altered retroactively without the alteration of all subsequent blocks and the consensus of the network. This allows the participants to verify and audit transactions inexpensively. A blockchain database is managed autonomously using a peer-to-peer network and a distributed timestamping server. They are authenticated by mass collaboration powered by collective self-interests. The result is a robust workflow where participants’ uncertainty regarding data security is marginal.
Further Reading:
https://en.wikipedia.org/wiki/Blockchain