Chain of block is called Blockchain.
“Blocks” on the blockchain are made up of digital pieces of information. A block containing about the transactions. Each transactions generate the one hash. A hash is a string of numbers and letters.
The hash depends not only on the transactions but the previous transaction's hash. A small change in the block then it creates a new hash.
Each block refers to the previous block and together make the blockchain. A blockchain is effective as it is spread over many computers, each of which have a copy of the blockchain.
Each block of the chain comprises a cryptographic hash, transaction or timestamp of the previous block.
Blockchain is the only technology till date which is quite hard to hack because it is secure and reliable.
In Blockchain, the data is scattered over various computers on a peer-to-peer network and the data is connected to each other with hashing, i.e. unique code.
For example, voting system is secure based on Blockchain. If any person try to modify the vote then the error occur in block. And it will be directly responded to the server. Thus the votes are fully secure.
It becomes impossible for the hackers to retrieve the data in Blockchain.