A blockchain glossary for programmers.

Source: ISO 22739:2020 (en) Blockchain and distributed ledger technologies — Vocabulary

anything that has value to a stakeholder
structured data comprising block data (3.3) and a block header

block data
structured data comprising zero or more transaction records or references to transaction records
block header
structured data that includes a cryptographic link to the previous block unless there is no previous block

Note 1 to entry: A block header can also contain a timestamp, a nonce, and other DLT platform specific data, including a hash value of corresponding transaction records.
block reward
reward given to miners or validators after a block is confirmed in a blockchain system

Note 1 to entry: A reward can be in the form of a token or cryptocurrency.
organized in an append-only, sequential chain using cryptographic links

Note 1 to entry: Blockchains are designed to be tamper resistant and to create final, definitive and immutable ledger records.
blockchain system
system that implements a blockchain

Note 1 to entry: A blockchain system is a type of DLT system.
accepted by consensus for inclusion in a distributed ledger
confirmed block
block that has been confirmed
confirmed transaction
transaction that has been confirmed
agreement among DLT nodes that 1) a transaction is validated and 2) that the distributed ledger contains a consistent set and ordering of validated transactions

Note 1 to entry: Consensus does not necessarily mean that all DLT nodes agree.

Note 2 to entry: The details regarding consensus differ among DLT designs and this is a distinguishing characteristic between one design and another.
consensus mechanism
rules and procedures by which consensus is reached
digital asset implemented using cryptographic techniques
crypto-asset designed to work as a medium of value exchange

Note 1 to entry: Cryptocurrency involves the use of decentralized control and cryptography to secure transactions, control the creation of additional assets, and verify the transfer of assets.
cryptographic hash function
function mapping binary strings of arbitrary length to binary strings of fixed length, such that it is computationally costly to find for a given output an input that maps to the output, it is computationally infeasible to find for a given input a second input that maps to the same output, and it is computationally infeasible to find any two distinct inputs that map to the same output

Note 1 to entry: Computational feasibility depends on the specific security requirements and environment.
cryptographic link
reference, constructed using a cryptographic hash function technique, that points to data

Note 1 to entry: A cryptographic link is used in the block header to reference the previous block in order to create the append-only, sequential chain that forms a blockchain.
discipline that embodies the principles, means, and methods for the transformation of data in order to hide their semantic content, prevent their unauthorized use, or prevent their undetected modification
decentralized application (DApp)
application that runs on a decentralized system
decentralized system
distributed system wherein control is distributed among the persons or organizations participating in the operation of the system

Note 1 to entry: In a decentralized system, the distribution of control among persons or organizations participating in the system is determined by the system’s design.
digital asset
asset that exists only in digital form or which is the digital representation of another asset
digital signature
data which, when appended to a digital object, enable the user of the digital object to authenticate its origin and integrity
distributed ledger
ledger that is shared across a set of DLT nodes and synchronized between the DLT nodes using a consensus mechanism

Note 1 to entry: A distributed ledger is designed to be tamper resistant, append-only and immutable containing confirmed and validated transactions.
distributed ledger system
system that implements a distributed ledger
distributed ledger technology (DLT)
technology that enables the operation and use of distributed ledgers
distributed ledger technology account (DLT account)
representation of an entity participating in a transaction

Note 1 to entry: A smart contract, digital asset, or one or more private keys, for example, can be associated with a DLT account.
distributed ledger technology address (DLT address)
value that identifies a DLT account participating in a transaction
distributed ledger technology network (DLT Network)
network of DLT nodes which make up a DLT system
distributed ledger technology node
device or process that participates in a network and stores a complete or partial replica of the ledger records
distributed ledger technology oracle (DLT oracle)
service that updates a distributed ledger using data from outside of a DLT system

Note 1 to entry: DLT oracles are useful for smart contracts that cannot access sources of data external to the DLT system.
distributed ledger technology platform (DLT platform)
set of processing, storage and communication entities which together provide the capabilities of the DLT system on each DLT node
distributed ledger technology user (DLT User)
entity that uses services provided by a DLT system
distributed system
system in which components located on networked computers communicate and coordinate their actions by interacting with each other
double spending
failure of a DLT platform where the control of a token or crypto-asset is incorrectly transferred more than once

Note 1 to entry: Double-spending is most often associated with cryptocurrency.
item inside or outside an information and communication technology system, such as a person, an organization, a device, a subsystem, or a group of such items that has recognizably distinct existence
oss of ability to perform as required
fault tolerance
ability of a functional unit to continue to perform a required function in the presence of faults or errors
genesis block
first block in a blockchain

Note 1 to entry: A genesis block has no previous block and serves to initialize the blockchain.
hard fork
change to a DLT platform in which new ledger records or blocks created by the DLT nodes using the new version of the DLT platform are not accepted as valid by DLT nodes using old versions of the DLT platform

Note 1 to entry: If not adopted by all DLT nodes, a hard fork can result in a ledger split.

Note 2 to entry: In some contexts, the terms "hard fork" and "fork" are sometimes used for a ledger split that results from a hard fork of a DLT platform.
hash value
string of bits which is the output of a cryptographic hash function
property wherein ledger records cannot be modified or removed once added to a distributed ledger

Note 1 to entry: Where appropriate, immutability also presumes keeping intact the order of ledger records and the links between the ledger records
ability of two or more systems or applications to exchange information and to mutually use the information that has been exchanged
leaf node
node that has no child nodes
information store that keeps records of transactions that are intended to be final, definitive and immutable
ledger record
record containing transaction records, hash values of transaction records, or references to transaction records recorded on a distributed ledger
ledger split
creation of two or more different versions of a distributed ledger originating from a common starting point with a single history
Merkle root
root node of a Merkle tree
Merkle tree
tree data structure in which every leaf node is labelled with the hash value of a data element and every non-leaf node is labelled with the hash value of the labels of its child nodes
DLT node which engages in mining
activity, in some consensus mechanisms, that creates and validates blocks or validates ledger records

Note 1 to entry: Participation in mining is often incentivized by block rewards and transaction fees.
elementary component from which a data structure is built
number or bit string used once in a set of cryptographic operations

Note 1 to entry: A nonce is often random or pseudo-random. It is commonly used to guard against replay attacks, where a message is captured and re-sent by a malicious actor. In some blockchain systems it is used to modulate mining during the generation of a new block and is stored in the block header
related to a blockchain system, but located, performed, or run outside that blockchain system
located, performed, or run inside a DLT system
relating to, using, or being a network of equal peers that share information and resources with each other directly without relying on a central entity
requiring authorization to perform a particular activity or activities
permissioned distributed ledger system (permissioned DLT system)
DLT system in which permissions are required
not requiring authorization to perform any particular activity
permissionless distributed ledger system (permissionless DLT system)
DLT system that is permissionless
private distributed ledger system (private DLT system)
DLT system that is accessible for use only to a limited group of DLT users

Note 1 to entry: Public and private categories apply to DLT users, and permissioned and permissionless categories apply to DLT users and those entities that administer or operate the DLT system.
private key
key of an entity's asymmetric key pair that is kept secret and which should only be used by that entity
produce a smaller replica of a distributed ledger by removing all transaction records meeting specified criteria while ensuring that those transactions can be restored with integrity if needed
public distributed ledger system (public DLT system)
DLT system which is accessible to the public for use
public key
key of an entity's asymmetric key pair which can be made public
public-key cryptography
cryptography in which a public key and a corresponding private key are used for encryption and decryption, or are used for verifying digital signatures and digitally signing, respectively
information created, received and maintained as evidence and as an asset by an organization or person, in pursuit of legal obligations or in the transaction of business

Note 1 to entry: This term applies to information in any medium, form or format.
reward system incentive mechanism
method of offering reward for some activities concerned with the operation of a DLT system

Note 1 to entry: An example of a reward is a block reward (3.5).
root node
node that has no parent node
shared ledger
distributed ledger in which the content of ledger records is accessible by multiple entities
blockchain system that interoperates with a separate associated blockchain system to perform a specific function in relation to the associated blockchain system

Note 1 to entry: By convention the original chain is normally referred to as the "main chain", while any additional blockchains which allow DLT users to transact on the main chain are referred to as "sidechains”.
smart contract
computer program stored in a DLT system wherein the outcome of any execution of the program is recorded on the distributed ledger

Note 1 to entry: A smart contract can represent terms in a contract in law and create a legally enforceable obligation under the legislation of an applicable jurisdiction.
soft fork
change to a DLT platform that is not a hard fork and in which some records or blocks created by the DLT nodes using the old version of the DLT platform are not accepted as valid by DLT nodes using new versions of the DLT platform
logically separate chain that can form part of a blockchain system

Note 1 to entry: A subchain allows for data isolation and confidentiality.
time variant parameter which denotes a point in time with respect to a common time reference
digital asset that represents a collection of entitlements
smallest unit of a work process, which is one or more sequences of actions required to produce an outcome that complies with governing rules

Note 1 to entry: Where appropriate, transaction is understood more narrowly, as the smallest unit of a work process related to interactions with blockchains or distributed ledgers.
transaction fee
fee paid to miners or validators for inclusion of a transaction in a distributed ledger
transaction record
record documenting a transaction of any type

Note 1 to entry: Transaction records can be included in, or referred to, in a ledger record.

Note 2 to entry: Transaction records can include the result of a transaction.
degree to which a user or other stakeholder has confidence that a product or system will behave as expected by that user or other stakeholder
status of an entity when its required integrity conditions have been checked

Note 1 to entry: For example, in a DLT system, a transaction, ledger record, or block can be validated.
function by which a transaction, ledger record, or block is validated
entity in a DLT system that participates in validation

Note 1 to entry: In some DLT systems the DLT node that has the role of validator can digitally sign a ledger record or block.