What is the 'Blockchain'?

The blockchain is an open, decentralized ledger that allows for peer-to-peer transfers, verified by other members of the blockchain.

Key features of the blockchain:

No central authority - no single fault point to take down the network
Peer-to-peer transfers
The blockchain database is shared by all nodes participating in the system
The blockchain has records of every transfer ever made
Transfers cannot be altered after the fact
Transparent ledger, off-ledger data transfers are not possible

How it works:

A wants to send data to B
The transfer is represented online as a 'block'
The 'block' is broadcast to the other members of the network
The network members approve (or deny if fraudulent) the transfer
The 'block' is added to the 'chain'
B receives data from A

The blockchain is most commonly associated with Bitcoin (and other cryptocurrencies) but there are hopes that it will eventually be used to reform the electoral process, bank transfers, contracts, intellectual property rights, retail and land registry.