Its name itself is derived from block and chain, which means chain formation of blocks. These blocks contains cryptographic data mapping of previous block and does timestapping—securely tracking the time and date of documents. It helps in transaction of data between two parties. It totally restricts any data modification with the help of strong cryptography.
It is “an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way”. For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network cumulatively under the protocol for inter-node communication and validating new blocks. Once the data is recorded, then the data from a single block cannot be altered. In order to alter the data it requires all subsequent blocks from consensus of the network majority. As the blockchains data is unaltered, it is securely used for cryptocurrency.
History: 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. The bitcoin design has inspired other applications.