A blockchain, originally block chain, is a growing list of records, called blocks, that are linked using cryptography. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree). By design, a blockchain is resistant to modification of its data. This is because once recorded, the data in any given block cannot be altered retroactively without alteration of all subsequent blocks.
"Blockchain is one of the most exciting inventions in human history."
“Bitcoin transactions are stored on the blockchain.”
“Transactions can be verified by using a blockchain explorer.”
“Put it on the blockchain.”
Definition(s) from the Web
The block chain is a public record of Bitcoin transactions in chronological order. The block chain is shared between all Bitcoin users. It is used to verify the permanence of Bitcoin transactions and to prevent double spending. Source
A block chain is a transaction database shared by all nodes participating in a system based on the Bitcoin protocol. A full copy of a currency’s block chain contains every transaction ever executed in the currency. With this information, one can find out how much value belonged to each address at any point in history. Every block contains a hash of the previous block. This has the effect of creating a chain of blocks from the genesis block to the current block. Each block is guaranteed to come after the previous block chronologically because the previous block’s hash would otherwise not be known. Each block is also computationally impractical to modify once it has been in the chain for a while because every block after it would also have to be regenerated. These properties are what make bitcoins transactions irreversible. The block chain is the main innovation of Bitcoin. Source
Blockchain is a cryptographically secured, time-stamped, public and distributed database of every bitcoin transaction that has ever occurred on the network. “Distributed” here means that the information in the blockchain is broadcast to and recorded by every node in the network. There is no one central database. Any user can refer to this list of transactions and check exactly what how many bitcoins have ever belonged to any specific address at any point in time. This way the system is transparent, double-spending is prevented, and there is no need for a trusted central authority. The bitcoin blockchain is supported by the efforts of many miners: users who put computing power to the task of solving a mathematical problem that will reward them with bitcoins, while at the same time producing the hashes that secure the blocks of data in the chain. The hashes are cryptographically produced strings of data that make the info in the blockchain virtually impossible to tamper with. Source
A blockchain, originally block chain, is a growing list of records, called blocks, that are linked using cryptography. Each block contains a cryptographic hash of the previous block, a timestamp, and transaction data (generally represented as a Merkle tree). By design, a blockchain is resistant to modification of its data. This is because once recorded, the data in any given block cannot be altered retroactively without alteration of all subsequent blocks. For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for inter-node communication and validating new blocks. Although blockchain records are not unalterable, blockchains may be considered secure by design and exemplify a distributed computing system with high Byzantine fault tolerance. The blockchain has been described as “an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way”. The blockchain was invented by a person (or group of people) using the name Satoshi Nakamoto in 2008 to serve as the public transaction ledger of the cryptocurrency bitcoin. The identity of Satoshi Nakamoto remains unknown to date. 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 and blockchains that are readable by the public and are widely used by cryptocurrencies. The blockchain is considered a type of payment rail. Private blockchains have been proposed for business use but Computerworld called the marketing of such privatized blockchains without a proper security model “snake oil”. However, others have argued that permissioned blockchains, if carefully designed, may be more decentralized in practice than permissionless ones. Source