n. ~ An open-source technology that supports trusted, immutable records of transactions stored in publicly accessible, decentralized, distributed, automated ledgers.
Because blockchain technology relies on disintermediated access to multiple copies of distributed ledgers, the need for a centralized authority (such as a bank) to approve transactions is not necessary. Trust in the security of a blockchain is based on the notion that each block inherits the root hash of all previous transactions, and altering a given transaction would require simultaneous alteration of all subsequent blocks in all copies of the distributed ledgers created since the transaction took place. Blockchain technology is designed to confirm records' integrity, existence at a certain point in time, and sequence to support their non-repudiation. Bitcoin is an example of a technology that uses blockchain technology to store information about cryptocurrency.
- Back et al. 2010 (†832 s.v. "3.1 Definitions"): A blockchain is a well-ordered collection of blocks, on which all users must (eventually) come to consensus. This determines the history of asset control and provides a computationally unforgeable time ordering for transactions.
- Bitcoin Developer Glossary 2017 (†791 s.v. "Block Chain"): A chain of blocks with each block referencing the block that preceded it. The most-difficult-to-recreate chain is the best block chain.
- Bitcoin Group  (†846 s.v. "Blockchain"): The full list of blocks that have been mined since the beginning of the bitcoin cryptocurrency. The blockchain is designed so that each block contains a hash drawing on the blocks that came before it. This is designed to make it more tamperproof. · To add further confusion, there is a company called Blockchain, which has a very popular blockchain explorer and bitcoin wallet.
- Bitcoin Wiki Vocabulary  (†796 s.v. "Blockchain"): Each block includes the difficult-to-produce verification hash of the previous block. This allows each subsequent block to be linked to all previous blocks. These blocks which are linked together for the purpose of verifying transactions within blocks is called the block chain.
- Blockchain Technologies 2016 (†789 s.v. "Blockchain"): A blockchain is a type of distributed ledger, comprised of unchangable, digitally recorded data in packages called blocks (rather like collating them on to a single sheet of paper). Each block is then ‘chained’ to the next block, using a cryptographic signature. This allows block chains to be used like a ledger, which can be shared and accessed by anyone with the appropriate permissions.
- BlockchainHub Glossary (†807 s.v. "Blockchain"): Shared, trusted, public ledger of transactions, that everyone can inspect but which no single user controls. It is a cryptographed, secure, tamper resistant distributed database. It solves a complex mathematical problem to exist. A blockchain is a perfect place to store value, identities, agreements, property rights, credentials, etc. Once you put something like a Bitcoin into it, it will stay there forever. It is decentralized, disintermediated, cheap and censorship resistant. Applications of Blockchain: Bitcoin (cryptocurrency), Namecoin (wants to replace the entire DNS system of the Internet), or Blocksign (non-disclosure agreements at very low costs of only a few cents), Ethereum (Turing complete Virtual Machine where you can run any smart contract); Any centralized service like eBay, Dropbox can potentially be built in a decentralized way using blockchain technology, considerably lowering transaction costs.
- Condos et al. 2016 (†819 p.3): A blockchain is an electronic ledger (register) of digital records, events, or transactions that are represented in condensed form known as a hash (digital security feature), authenticated, and maintained through a “distributed” or “shared” network of participants using a group consensus protocol (multiple users).
- Deloitte Insights 2016 (†801 p.46): (or blockchain technology). The generic name for the family of technologies that provide the same functionality as bitcoin, but which use different approaches to realising the functionality, via alternate algorithms for example, a family of solutions.
- Garfinkel et al. 2016 (†823 p.1): At a very high level, the blockchain is a decentralized ledger, or list, of all transactions across a peer-to-peer network. This is the technology underlying Bitcoin and other cryptocurrencies, and it has the potential to disrupt a wide variety of business processes.
- Gartner IT Glossary (†298 s.v. "blockchain"): Blockchain is a type of distributed ledger in which value exchange transactions (in bitcoin or other token) are sequentially grouped into blocks. Each block is chained to the previous block and immutably recorded across a peer-to-peer network, using cryptographic trust and assurance mechanisms. Depending on the implementation, transactions can include programmable behavior.
- ISO TC307 (Japan). 2017 (†857 p.8): a group of transactions self-secured by connected hashes (3.4) in a distributed network (3.9).
- ISO TC307 N55 (France). 2017 (†858 ): Bound chain of blocks validated by consensus and stored within a distributed ledger.
- ISO TC307 N67 (United Kingdom). 2017. (†841 p.1): implementation of distributed ledger technology that records blocks of data in chain transactions and exchanges that take place in a peer-to-peer network.
- ISO TC307 N67 (United Kingdom). 2017. (†841 p.1 ): ever-extending series of blocks that grows as new transactions are confirmed as part of a new block. · Note: Each new block is chained to the existing blockchain by a cryptographic technique.
- Pfeffer  (†844 s.v. "Blockchain"): An Ethereum Blockchain is a distributed database that maintains a continuously-growing list of records called *Blocks* secured from tampering and revision. Each Block contains a timestamp and a link to a previous Block in a Merkle tree structure.
- Scaling Bitcoin  (†845 s.v. "Blockchain / Chain"): A public ledger of all confirmed transactions in a form of a tree of all valid blocks (including orphans). Most of the time, "blockchain" means the main chain, a single most difficult chain of blocks. Blockchain is updated by mining blocks with new transactions. Unconfirmed transactions are not part of the blockchain. If some clients disagree on which chain is main or which blocks are valid, a fork happens.
- Seibold et al. 2016 (†821 p.1): A type of distributed ledger database that maintains a continuously growing list of transaction records ordered into blocks with various protections against tampering and revisions.
- Bitcoin Glossary 2017 (†812 s.v. "Blockchain"): The full list of blocks that have been mined since the beginning of the bitcoin cryptocurrency. The blockchain is designed so that each block contains a hash drawing on the blocks that came before it. This is designed to make it more tamperproof. · To add further confusion, there is a company called Blockchain, which has a very popular blockchain explorer and bitcoin wallet. (†2080)
- Blockchain 2016 (†768 ): Blockchain and electronic distributed ledger technologies are an emerging peer-to-peer data base tool for managing and recording transactions. The technology behind blockchains is open source. ¶This new disruptive technology offers the prospect for sharing financial, legal, physical or electronic information more readily across multiple sites (nationally and internationall y) and from government to business or business to business. ¶Blockchain has the potential to support efficient and secure transactions and reduce process management issues across a range of economic sectors including: · government · consumer products and services · health · minerals and precious stones · financial services · real estate · business (†1941)
- Blockchain 2016 (†768 ): The purpose of the blockchain is to provide a trusted immutable record across a distributed cryptographic ledger network that stores a copy and validates each transaction on each node. ¶ The blockchain has been created to allow verification and immutable validation between peers, without the need of middlemen or 3rd parties. In practice, this means once data has been written to a blockchain no one, not even a system administrator, can change it. (†1942)
- Buterin  (†818 s.v. "Mining"): Bitcoin's decentralized consensus process requires nodes in the network to continuously attempt to produce packages of transactions called "blocks". The network is intended to create one block approximately every ten minutes, with each block containing a timestamp, a nonce, a reference to (i.e., hash of) the previous block and a list of all of the transactions that have taken place since the previous block. Over time, this creates a persistent, ever-growing, "blockchain" that continually updates to represent the latest state of the Bitcoin ledger. (†2177)
- Casey 2016 (†877 ): We finally have the conceptual framework for [a distributed rust management system], one in which trust need no longer be invested in a third-party intermediary but managed in a distributed manner across a community of users incentivized to protect a public good. Blockchain technology and the spinoff ideas it has spawned provide us with the best chance yet to solve the age-old problem of the Tragedy of the Commons. ¶ This technology creates a mechanism by which people and institutions that would not otherwise trust each other can agree, in a constantly updated process, on a common record of events. The blockchain is an unbroken, sequential ledger that’s replicated in multiple copied versions and stored on multiple, independent computers. Each node runs the same open source software that dictates how to update the shared ledger with new transactions and how to arrive at a consensus on whether those updates are valid. (†2630)
- Condos et al. 2016 (†819 p.6): The blockchain is a continually-growing digital register of transactions. Each set of transactions (the number of which is prescribed by the protocol) is considered a block in the chain, and the register as a whole is the blockchain. (†2133)
- Crowe 2016 (†771 ): Blockchains are ledgers (like Excel spreadsheets), but they accept inputs from lots of different parties. The ledger can only be changed when there is a consensus among the group. That makes them more secure, and it means there's no need for a central authority to approve transactions. ¶ It's a spreadsheet [that has] special qualities that make it better than traditional databases. [It's] shared publicly, decentralized, secure, trusted, and automated. (†1948)
- Gaur 2016 (†772 ): [Blockchain is] a cryptographic database technology that is known to the masses through its association with cybercurrency (bitcoins, altcoins). In fact, the technology itself, when disassociated with currency, has the promise to change the world (once again) as we know it. Blockchain technology has the power to provide a platform to remove middlemen, regardless of the industry, and it does not end there. There are real business models emerging that are backed by this technology. Those business models, based on such concepts as cyber trust, cyber equity, interledger, and cyber identity, all reflect the aim to establish networking that is trustless and yet secure (†1949)
- Gaur 2016 (†772 ): Blockchain promises systemic security as a trust currency. Economic transactions on a distributed ledger can be programmed to record virtually anything of value: your identity, a will, a deed, a title, a license, intellectual property, and also almost any type of financial instrument. (†1951)
- Norton 2016 (†770 ): At a time when companies face new challenges in data management and security, [blockchain is] emerging as a way to let companies make and verify transactions on a network instantaneously without a central authority. (†1943)
- Norton 2016 (†770 ): A blockchain is a data structure that makes it possible to create a digital ledger of transactions and share it among a distributed network of computers. It uses cryptography to allow each participant on the network to manipulate the ledger in a secure way without the need for a central authority. ¶Once a block of data is recorded on the blockchain ledger, it’s extremely difficult to change or remove. When someone wants to add to it, participants in the network — all of which have copies of the existing blockchain — run algorithms to evaluate and verify the proposed transaction. If a majority of nodes agree that the transaction looks valid — that is, identifying information matches the blockchain’s history — then the new transaction will be approved and a new block added to the chain. (†1945)
- Norton 2016 (†770 ): The term blockchain today usually describes a version of this distributed ledger structure and distributed consensus process. There are different blockchain configurations that use different consensus mechanisms, depending on the type and size of the network and the use case of a particular company. (†1946)
- Piasecki 2017 (†815 s.v. 2017-02-20 "Blockchain Terminology-a dev): · A Blockchain is a collection of Blocks refering to one another in a linear sequence all the way to a Genesis Block. Because of how the chain is created, any change to any Block in the sequence would invalidate all of the Blocks that came afterwards. This is one of the core features of a Blockchain known as Immutability. · If two or more Blocks refer to the same previous Block Hash, this is known as a Fork. In most systems, only one of those Blocks will be considered valid, usually the one that will end up in the longest branch. · The term "Blockchain" is also used to refer to the projects that use Blockchains. Bitcoin is a Blockchain project that contains the Bitcoin Blockchain. This term was popularized in mid-2015 by large enterprises such as Overstock and NASDAQ wanting to use the then called "Bitcoin technology" without using the term "Bitcoin" due to its various connotations. (†2098)
- Stubbs and Ankeemana 2016 (†773 ): Block chains are distributed databases, using sophisticated cryptography and consensus to ensure end-to-end transactional integrity without the need for a trusted central party. ¶ Public blockchains deliver participants an immutable history of all transactions stored on the database. This permanent record, visible to all actors, overcomes the ‘double spend’ problem of digital goods by enabling buyers and sellers to instantaneously verify that funds and goods are available when executing a transaction. (†1952)
- Stubbs and Ankeemana 2016 (†773 ): A public blockchain mirrors this distributed trust model. It’s often called a distributed ledger, a fancy way of saying that every record is shared by everyone who’s involved in any given blockchain. Participation is open to any interested party and updates can be triggered by anyone but need to be validated by a majority of participants before they’re written to the blockchain. And, as every update is dependent on one earlier in the ledger, it creates a lineage of transactions; a “chain” of “blocks”, if you will. ¶ The nature of this lineage makes the ledger inviolate. Because updates are chained, dependent on prior ones, and validated by consensus, falsifying prior transactions is impossible without controlling a majority of peers within the blockchain. (†1954)
- Stubbs and Ankeemana 2016 (†773 ): Blockchain is important because it represents the latest in an ongoing trend towards decentralization, disruption, and disintermediation. It promises to disrupt business models and processes reliant on centralized trust. (†1958)
- Stubbs and Ankeemana 2016 (†773 ): Blockchain represents a technical solution for the decentralization of trust. Industries, processes, or business models that are heavily reliant on the centralization of trust for either competitive advantage, sustainability, or success are all under threat. Those who operate in these spaces need to start strategizing now as to how they will either mitigate the risk blockchain presents or take advantage of the disruptive nature of blockchain to radically simplify their operations. (†1959)
- Walport 2016 (†802 p.17): A block chain is a type of database that takes a number of records and puts them in a block (rather like collating them on to a single sheet of paper). Each block is then ‘chained’ to the next block, using a cryptographic signature. This allows block chains to be used like a ledger, which can be shared and corroborated by anyone with the appropriate permissions. · There are many ways to corroborate the accuracy of a ledger, but they are broadly known as consensus (the term ‘mining’ is used for a variant of this process in the cryptocurrency Bitcoin). If participants in that process are preselected, the ledger is permissioned. If the process is open to everyone, the ledger is unpermissioned. · The real novelty of block chain technology is that it is more than just a database — it can also set rules about a transaction (business logic) that are tied to the transaction itself. This contrasts with conventional databases, in which rules are often set at the entire database level, or in the application, but not in the transaction. (†2057)
- Walport 2016 (†802 p.34): What is ‘the block chain’? A block is simply a list of payments. A block chain is a list of blocks, each one referring back to the one that went before. However, when people talk about the block chain, they tend to mean the collection of technologies and techniques that underpin the Bitcoin system, which other projects have used as inspiration because they solve unrelated problems in finance and elsewhere. (†2123)
- Wood 2014 (†803 p.2): In order to form a consensus as to which path, from root (the genesis block) to leaf (the block containing the most recent transactions) through this tree structure, known as the blockchain, there must be an agreed-upon scheme. (†2048)