What is a ‘Blockchain’?
A blockchain is a decentralized, digitized, public ledger of all cryptocurrency transactions. It grows ever bigger as completed blocks (the most recent transactions) are added and recorded to the ledger. It follows a chronological order and as a result, allows anyone to easily follow & keep track of any digital currency transactions without the need of having a central record keeper. Each node, which is a computer that is connected to the network, will automatically download a copy of the blockchain.
You can think of Information on a blockchain existing as a shared database, this means it has the advantage of not being stored in any single location. As a result, there is never a centralized version that a hacker could corrupt and by hosting all the data on millions of computers at the same time, the data is accessible to anyone with an internet connection - making it easily verifiable.
Originally it was developed as the accounting method for the first virtual currency: Bitcoin.