Blockchain is one of the most important invention science the internet itself. It is a distributed database that maintains a continuously growing list of ordered records called blocks. Each block contains a timestamp and a link to a previous block. Blockchains are secure by design and an example of a distributed computing system with high byzantine fault tolerance.
The first blockchain was conceptualised by Satoshi Nakamoto in 2008 and implemented the following year as a core component of the digital currency bitcoin, where it serves as the public ledger for all transactions. Through the use of a peer-to-peer network and a distributed timestamping server, a blockchain database is managed autonomously. The invention of the blockchain for bitcoin made it the first digital currency to solve the double spending problem, without the use of a trusted authority or central server. Blockchains are “an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way. By design, blockchains are inherently resistant to modification of the data — once recorded, the data in a block cannot be altered retroactively.
When a new transaction is made with bitcoin, that transaction is broadcast to thousands of nodes that comprise bitcoin network. Bitcoin network has bitcoin minors that work to process the transactions adding them to ledger. All these nodes have copies of the same ledger and all see same the transaction. Once certain amount of transactions are added, they become a block. That block is protected by cryptography, connects to previous block that connects to its previous block all the way back to the first bitcoin transaction ever creating a chain of blocks, hence the name blockchain.
Because these ledgers are open to all and have access to these ledgers and they are constantly crosschecking them, it is difficult for a hacker to temper with them as changing one will create discrepancy within the whole n/w. the decentralization makes the system even better. Blockchain creates concrete records of transaction that everyone can believe. It is a system that provides truth and transparency.
Understand How Blockchain works