Essentially, a blockchain is a distributed ledger in which transactions between any two or more parties are verified and permanently stored with the aid of cryptographic algorithms. It can be considered as a complete database stored on every individual system connected to a peer-to-peer network. Contained within this database is a record of how much of the currency each connected address or system has, as well as the transactions associated with that address or system. The distributed nature of the blockchain makes it impossible for any one entity to alter a record, or to submit falsified information because all transactions are automatically verified by other entities in the peer-to-peer network.
Due to its distributed nature, the blockchain system remains immune from outside interference and one of its main benefits is that it eliminates the uncertainty that often accompanies transactions. In other words, once you decide to enter into a transaction with someone, that transaction will be completed automatically by the system, thereby keeping the transaction honest.