Blockchain formation. The main chain (black) consists of the longest series of blocks from the genesis block (green) to the current block. Orphan blocks (purple) exist outside of the main chain.source
A blockchain is a distributed digital ledger used to record and cryptographically secure transactions across many computers- The records of these transactions are continuously synchronised on all participating computers. With blockchain technology, retroactive falsification of records becomes near impossible. Technology therefore enables trust in transactions and their records without relying on a central authority.
Blockchain technology was first introduced in a 2009 Whitepaper pdf 
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# Features
Blockchain is versatile: it is being widely considered as a way to manage financial transactions, asset transfers and regulatory obligations. In particular, blockchain is now seen by many as the future of land registration.
# Applications
Blockchains are potentially suitable for the recording of events, medical records, identity management, food traceability or voting.
Using the example of land registries, we can point here to some of the potential benefits:
- reduce property fraud (a growing concern for HM Land Registry), as each property would be uniquely coded and linked to a smart key which would be held only by the owner. - use so called ‘smart contracts’ = programmable contracts that self-execute when certain conditions are met - accelerate transactions, certainly not needed on the highly volatile financial markets, but useful for completing more quickly a land acquisition. The title to the property could be transferred to the purchaser automatically on receipt of funds into the vendor’s account. - speed up the registration process, as the ledger updates immediately. The so called "registration gap" would be eliminated. - cost savings for the transactions (lawyers) and for land registries
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# See also
# Sources
Blockchain on wikipedia, wiki
White-paper: Terrafirma - A global blockchain land trust framework (unpublished)