"Simply stated, blockchain is a program code technique that creates a secure, decentralized ledger (think database) of transactions and information. A blockchain can be public, like Bitcoin, or it can be private, like those that are developed by businesses for internal transactions and information sharing. Businesses already maintain detailed ledgers of their economic transactions, and these sources of information are centralized as the business controls what is recorded or removed on the ledger. Blockchain technology decentralizes that information by requiring multiple validations by independent sources before accepting a transaction as completed. Every time you send a Bitcoin to a friend the transaction is validated by multiple “nodes,” who must all agree that the transaction has occurred in order to have the transaction recorded on the public ledger (the transaction executes). This technique is why blockchain is so secure: if a party attempts to corrupt that transaction the other nodes wouldn't recognize it and it would not be added to the ledger. You also have a complete record of where you Bitcoin has been and who has used it.

"Why is this desirable? As technology and business becomes more complicated, so do our economic exchanges. We live in a global marketplace and we rely heavily on third-parties to facilitate a lot of the business we conduct (think governments and banks). These third parties often charge fees, can cause costly delays, have little or no transparency in their practice, and maintain their own transaction records that are often isolated from the other parties. Distributed ledger technology allows parties to create a secure and decentralized public ledger that allows the participants to monitor each and every transaction without a third-party to validate or facilitate the exchange. As one expert put it: “We can create a decentralized database that has the same efficiency of a monopoly without actually creating that central authority.”

SOURCE ARTICLE: 
https://www.minds.com/blog/view/795817221115650048