Blocktionary: A to Z Crypto and Blockchain Glossary

An attack in which one party controls most of a proof-of-work network’s hashpower (or a proof-of-stake network’s stake) and uses it to reverse its own recent transactions. Small coins are far more exposed than large ones.

A string of letters and numbers, often shown as a QR code, that tells the network where to send coins. Bitcoin addresses usually start with 1, 3 or bc1.

Free tokens sent to many wallets at once, usually to promote a project. Unsolicited airdrops are also a common bait in phishing.

The highest price an asset has ever traded at. Its opposite is the all-time low (ATL).

Any cryptocurrency other than Bitcoin. See our altcoins guide for the main types and what happened to the 2014 class.

Anti-money laundering: the laws that require exchanges and other providers to check customers and report suspicious activity.

Application-specific integrated circuit, a chip built for a single task. Bitcoin and Litecoin mining is now done almost entirely on ASIC machines.

A trade of one cryptocurrency for another, directly between two people, that either completes in full on both chains or not at all.

A long period of falling prices. A “bear” expects prices to drop; a “bull” expects them to rise.

The first cryptocurrency, described in a white paper published by Satoshi Nakamoto on 31 October 2008 and launched in January 2009. Our What is Bitcoin guide explains how it works.

A kiosk that exchanges cash or card payments for bitcoin. Fees are usually high, and the machines are heavily used in scams.

A unit equal to one-millionth of a bitcoin (100 satoshis). One BTC equals 1,000,000 bits.

A batch of transactions added to a blockchain in one go, together with a header that links it to the block before.

A website that lets you look up any public transaction, address or block. It can show information but cannot move or recover coins.

The new coins a miner receives for adding a block, plus transaction fees. On Bitcoin the new-coin part has been 3.125 BTC since April 2024.

A shared record of transactions stored as a chain of blocks, each one cryptographically tied to the last, so past entries cannot be quietly edited.

A service that moves tokens between blockchains, typically by locking them on one chain and issuing a matching token on another. Bridges have been the target of some of the largest hacks.

A centralised exchange, run by a company that holds customers’ funds and matches their orders.

The number of coins currently available to trade, excluding coins that are locked, burned or not yet issued.

Keeping private keys on a device or medium that never connects to the internet, such as a hardware wallet or a metal backup.

Each new block added after the one containing your transaction. More confirmations make a reversal less likely.

The rules a network uses to agree on which transactions are valid and in what order, for example proof of work or proof of stake.

Digital money secured by cryptography and recorded on a shared ledger instead of a single bank’s books.

Secretly using someone else’s computer or cloud account to mine cryptocurrency.

A wallet where a company holds the private keys for you. Convenient, but you rely on that company staying solvent and honest.

Decentralised autonomous organisation: a group that makes decisions through votes recorded on a blockchain, often weighted by token holdings.

A decentralised application whose core logic runs as smart contracts on a blockchain.

A decentralised exchange that lets users trade directly from their own wallets through smart contracts rather than through a company.

Decentralised finance: lending, trading and other financial services built from smart contracts.

A measure of how hard it is to find a valid block. Bitcoin adjusts it every 2,016 blocks to keep blocks about ten minutes apart.

A database copied across many computers that agree on its contents without a central owner. A blockchain is one kind.

Trying to spend the same coins twice. Preventing this without a central authority was the core problem Bitcoin solved.

An amount of cryptocurrency so small that sending it would cost more in fees than it is worth.

The standard most fungible tokens on Ethereum follow, so wallets and exchanges can handle them in the same way.

The native currency of the Ethereum network, used to pay transaction fees and to stake.

A blockchain launched in 2015 that runs general-purpose programs (smart contracts). It moved from proof of work to proof of stake in September 2022.

A platform for buying, selling or swapping cryptocurrencies, either for other coins or for ordinary money.

A website that gives away tiny amounts of cryptocurrency, often for viewing ads or solving puzzles. Payouts are small, and many faucets are low-quality or fraudulent.

Government-issued currency such as the euro or the dollar, valuable because the state declares it legal tender rather than because it is backed by a commodity.

Fear of missing out: buying in a hurry because prices are rising. Scammers exploit it deliberately.

A change to a blockchain’s rules or a split in its history. See hard fork and soft fork.

A computer that downloads every block and checks every rule independently, without trusting anyone else.

Interchangeable: one unit is as good as another, like two banknotes of the same value. NFTs are the opposite.

The unit Ethereum uses to measure the computing work a transaction needs. Fees are gas used multiplied by the price per unit.

The very first block of a blockchain. Bitcoin’s was created on 3 January 2009.

The scheduled cut by half of the new-coin reward per block. Bitcoin halves every 210,000 blocks, roughly every four years; the latest was in April 2024.

A rule change that older software will not accept. If some users refuse to upgrade, the chain can split into two, as Bitcoin Cash did in 2017.

A small dedicated device that stores private keys offline and signs transactions without exposing the keys to your computer.

A fixed-length fingerprint of any data, produced by a hash function. Change one character of the input and the hash changes completely.

How many hash attempts per second a miner or a whole network performs. Bitcoin’s is measured in exahashes per second (EH/s).

Crypto slang for holding coins long term regardless of price swings. It began as a misspelling of “hold” in a 2013 forum post.

A wallet whose keys sit on an internet-connected device such as a phone or a computer. Fine for small amounts, riskier for large ones.

Initial coin offering: selling a new token to the public to raise money. Many ICOs of 2017 and 2018 failed or were found to be unregistered securities sales.

The property that confirmed records are practically impossible to change after the fact.

Know your customer: identity checks that regulated platforms must carry out before letting you trade or withdraw.

A system built on top of a blockchain to make transactions faster or cheaper, settling back to the main chain. The Lightning Network is a Bitcoin example.

A record of who owns what. In crypto, the ledger is public and shared instead of being held privately by one bank.

A layer-2 payment network for Bitcoin (also usable with Litecoin) in which payments flow through channels and only the opening and closing hit the main chain.

How easily an asset can be bought or sold without moving its price. Small coins often have very little.

A Bitcoin offshoot launched in October 2011 with faster blocks and a cap of 84 million coins. Read more in What is Litecoin.

The coin’s price multiplied by its circulating supply. It is a quick size measure, not cash that could actually be withdrawn.

A server that locks up collateral to perform extra network tasks in return for rewards, a model made popular by Dash.

The waiting room of unconfirmed transactions that nodes hold until miners include them in a block.

The EU’s Markets in Crypto-Assets Regulation (Regulation (EU) 2023/1114), fully applicable from 30 December 2024, which sets licensing rules for crypto service providers and stablecoin issuers.

A participant who runs hardware to produce new blocks in a proof-of-work system and earns the block reward.

The process of finding valid blocks through proof of work. Doing it for profit now needs ASICs and cheap electricity; renting hashpower instead is covered in our cloud mining guide.

A group of miners who combine hashpower and share rewards in proportion to the work each contributed.

A wallet set-up that needs signatures from several keys (for example two of three) before coins can move.

Non-fungible token: a unique token, often linked to an image or other item. Owning one does not by itself give you copyright in that item.

Any computer that runs a blockchain’s software and relays transactions and blocks.

The number miners change over and over while searching for a block hash below the target.

Services that convert ordinary money into crypto (on-ramp) or crypto back into money (off-ramp). Our guide to buying bitcoin covers the regulated kind.

Software whose code anyone can read, copy and propose changes to. Bitcoin’s reference software is open source.

A service that feeds outside information, such as prices or sports results, into smart contracts.

A valid block that ends up outside the main chain because another block at the same height won. Many people now use “stale block” for this.

Peer to peer: users dealing directly with each other instead of through a central intermediary.

Keys printed on paper. Popular in the early years, now generally discouraged because they are easy to mishandle.

Fake websites, emails or messages that try to trick you into revealing passwords or recovery phrases.

Coins created for the founders before a cryptocurrency is publicly launched.

The secret number that proves ownership of coins and authorises spending them. Anyone who learns it can take the coins.

A consensus method in which validators lock up coins as collateral and are chosen to propose blocks; misbehaviour can cost them that stake.

A consensus method in which miners spend computing power to find a valid block hash. Bitcoin uses it.

A value derived from the private key that others can use to verify your signatures. Addresses are usually derived from it.

A scheme in which promoters hype a thinly traded coin, then sell to the buyers they attracted, leaving them with losses.

A square barcode used to share addresses and payment requests so they do not need to be typed.

When a project’s creators abandon it and take investors’ money, for example by draining a token’s trading pool.

The smallest unit of bitcoin: 0.00000001 BTC. There are 100 million satoshis in one bitcoin.

The pseudonymous author of the Bitcoin white paper and first software. Their real identity has never been proven.

A list of 12 or 24 words that can rebuild a wallet’s private keys. Keep it offline; never type it into a website or share it.

A 2017 Bitcoin upgrade that moved signature data into a separate part of the transaction, fixing malleability and making room for more transactions.

Holding your own private keys instead of trusting an exchange to hold coins for you.

The hash function used in Bitcoin mining and in many other parts of its design.

The gap between the price you expected and the price you actually got, common in fast markets or thin order books.

A program stored on a blockchain that runs automatically when its conditions are met.

A backwards-compatible tightening of the rules, which older nodes still accept. SegWit and Taproot were soft forks.

A token designed to keep a steady value, usually one US dollar or euro, backed by reserves or by other mechanisms.

Locking coins in a proof-of-stake network to help secure it in return for rewards.

A Bitcoin upgrade activated in November 2021 that improved privacy and flexibility for complex spending conditions.

A copy of a blockchain using coins with no value, so developers can test software safely.

The short symbol for a coin, such as BTC for bitcoin or LTC for litecoin.

A digital asset issued on an existing blockchain, as opposed to a coin with its own chain.

The amount paid to miners or validators to include a transaction. It depends on network demand and transaction size, not on the amount sent.

The requirement for crypto providers to pass sender and recipient details along with transfers. In the EU it applies under Regulation (EU) 2023/1113 from 30 December 2024.

Transaction ID: the unique hash that identifies a transaction on the blockchain, which you can look up in a block explorer.

Unspent transaction output: the model Bitcoin uses, in which your balance is a set of separate unspent pieces rather than one account number.

In proof of stake, a participant that proposes and checks blocks using staked coins.

How much and how fast a price moves. Crypto prices are far more volatile than most traditional assets.

Software or hardware that stores your keys and lets you send and receive coins. It holds the keys, not the coins themselves, which live on the blockchain.

An individual or entity holding a very large amount of a cryptocurrency, enough to move its price.

A document describing a project’s design. Bitcoin’s nine-page white paper set the template.

A cryptographic method of proving that something is true without revealing the underlying data. Zcash and several layer-2 networks use them.