Blockchain Glossary — 100 Essential Terms Every Business Leader and Developer Must Know

Account Abstraction (ERC-4337)

An Ethereum standard that allows smart contracts to act as wallets, enabling programmable transaction logic — including gasless transactions, session keys, social recovery, and batch operations without changing the core Ethereum protocol.

Address

A 42-character hexadecimal string (beginning with 0x on Ethereum) derived from a wallet's public key. Functions as the identifier for sending and receiving transactions on a blockchain.

AML (Anti-Money Laundering)

Regulatory framework requiring financial businesses to detect and prevent money laundering. Crypto exchanges and custodial businesses must implement AML programs under FinCEN's Bank Secrecy Act rules.

AMM (Automated Market Maker)

A type of decentralized exchange that uses liquidity pools and a mathematical formula (typically x·y=k) instead of an order book to price and execute trades. Uniswap, Curve, and Balancer are AMM protocols.

Audit (Smart Contract)

Independent security review of smart contract code by a specialized firm before production deployment. Identifies vulnerabilities including reentrancy, access control failures, integer errors, and economic attack vectors.

Blockchain

A distributed ledger where data is stored in cryptographically linked blocks validated by network consensus. Immutable, transparent, and decentralized — no single party can alter the historical record.

Bridge

Infrastructure enabling asset or message transfer between two separate blockchain networks. Examples: Arbitrum Bridge (Ethereum↔Arbitrum), Wormhole (multi-chain). High-value attack target due to concentrated locked assets.

CEX (Centralized Exchange)

A cryptocurrency exchange that holds user funds (custodial) and operates an internal order book. Examples: Coinbase, Binance, Kraken.

Chainlink

The dominant decentralized oracle network providing real-world data (price feeds, random numbers, external API data) to smart contracts. Used as the primary price oracle by Aave, Compound, Synthetix, and most major DeFi protocols.

DAO (Decentralized Autonomous Organization)

An organization governed by smart contracts and token holder voting, with no centralized management. Decisions made through on-chain proposals and votes executed automatically after a timelock.

dApp (Decentralized Application)

An application with its business logic running on a blockchain via smart contracts rather than a centralized server. The frontend may be centralized; the core logic is on-chain.

DeFi (Decentralized Finance)

Financial services — lending, trading, saving, insurance — running on blockchain smart contracts without traditional financial intermediaries.

DEX (Decentralized Exchange)

A cryptocurrency exchange where trading occurs via smart contracts without a custodial party holding user funds. Users trade directly from their wallets.

EIP (Ethereum Improvement Proposal)

A formal proposal to change the Ethereum protocol or establish standards. Notable EIPs: EIP-20 (ERC-20 token standard), EIP-721 (NFT standard), EIP-1559 (fee market reform), EIP-4337 (account abstraction).

ERC-20

The Ethereum token standard for fungible tokens. Defines the interface (transfer, approve, allowance, balanceOf, totalSupply) that any fungible token must implement for interoperability with wallets and DeFi protocols.

ERC-721

The Ethereum standard for non-fungible tokens (NFTs). Each token has a unique ID and owner. Defines ownerOf, safeTransferFrom, getApproved, and tokenURI functions.

ERC-1155

A multi-token standard supporting both fungible and non-fungible tokens in a single contract. Enables batch transfers for gas efficiency. Standard for gaming items and multi-edition art.

EVM (Ethereum Virtual Machine)

The runtime environment executing smart contracts on Ethereum and all EVM-compatible chains (Polygon, Arbitrum, Avalanche C-Chain, BNB Chain, etc.).

Externally Owned Account (EOA)

A blockchain account controlled by a private key — as opposed to a contract account (controlled by smart contract code). MetaMask manages EOAs. EOAs initiate transactions; contracts can only respond to calls.

FinCEN (Financial Crimes Enforcement Network)

US Treasury bureau responsible for enforcing the Bank Secrecy Act. Crypto businesses acting as Money Services Businesses (MSBs) must register with FinCEN and implement AML programs.

Flash Loan

A DeFi primitive allowing borrowing of any amount of assets within a single transaction, with no collateral required — as long as the loan is repaid by the end of the same transaction. Used for arbitrage, liquidations, and (maliciously) oracle manipulation attacks.

Foundry

A fast, portable smart contract development framework written in Rust. Tools: forge (compile/test), cast (interact), anvil (local node), chisel (REPL). The current professional standard for Solidity development.

Gas

The unit measuring computational work on the Ethereum network. Each EVM operation has a fixed gas cost. Total transaction cost = gas used × gas price (in Gwei).

Howey Test

The four-part test from SEC v. W.J. Howey Co. (1946) determining whether an asset is a security: (1) investment of money, (2) in a common enterprise, (3) with expectation of profits, (4) primarily from others' efforts.

HSM (Hardware Security Module)

A physical device that generates, stores, and uses cryptographic keys without exposing key material to software. Required for production exchange hot wallets. FIPS 140-2 Level 3 is the enterprise standard.

Impermanent Loss

The loss experienced by an AMM liquidity provider compared to simply holding the two tokens. Occurs because the AMM rebalances the ratio as prices change, resulting in the LP holding more of the declining asset.

IPFS (InterPlanetary File System)

A content-addressed distributed storage system. Files are identified by their content hash (CID). Used for storing NFT metadata and images — the NFT contract stores the IPFS URI.

L1 (Layer 1)

The base blockchain protocol (Ethereum, Bitcoin, Solana). All security guarantees ultimately derive from the L1 consensus mechanism.

L2 (Layer 2)

A protocol built on top of an L1 that processes transactions off-chain and settles proofs to the L1. Provides higher throughput and lower cost while inheriting L1 security. Examples: Arbitrum, Optimism, zkSync, Polygon PoS.

Liquidity Mining

A DeFi incentive mechanism where a protocol distributes its governance or utility tokens to users who provide liquidity to its pools. Used to bootstrap initial TVL.

MEV (Maximal Extractable Value)

Value extracted by validators or searchers by reordering, inserting, or excluding transactions within a block. Includes: arbitrage, liquidation front-running, sandwich attacks.

Merkle Tree

A binary tree of hash values where each leaf node contains a data hash and each internal node contains the hash of its children. The root hash (Merkle root) summarizes all data in the tree. Used in blockchain block headers and NFT allowlist verification.

Multi-Sig (Multi-Signature)

A wallet requiring M-of-N private key signatures to authorize any transaction. Gnosis Safe is the industry-standard multi-sig implementation. Used for DAO treasuries, exchange admin keys, and protocol governance.

Non-Custodial

A wallet or service where the user controls their own private keys. The service provider cannot access or recover user funds. Examples: MetaMask, Coinbase Wallet (self-custody mode).

NFT (Non-Fungible Token)

A unique blockchain record proving ownership of a specific item. Implemented as ERC-721 or ERC-1155 on Ethereum. Each NFT has a unique token ID distinguishing it from all other tokens.

Oracle

A service that brings off-chain data (prices, events, random numbers, external API data) onto the blockchain. Blockchain smart contracts cannot access external data without oracles. Chainlink is the dominant oracle network.

Proof of Stake (PoS)

A consensus mechanism where validators lock (stake) cryptocurrency as collateral to participate in block production. Validators are selected proportionally to their stake. Used by Ethereum post-Merge.

Proof of Work (PoW)

A consensus mechanism where miners compete to solve a cryptographic puzzle. The first to solve it adds the next block and earns the block reward. Used by Bitcoin. Energy-intensive by design — the energy expenditure makes attacks expensive.

Reentrancy

A smart contract vulnerability where an external call (to another contract or to the attacker's contract) allows the callee to re-enter the calling function before state updates complete. The DAO hack ($60M, 2016) was the most famous reentrancy exploit. Prevented by: checks-effects-interactions pattern and ReentrancyGuard.

Regulation A+

An SEC exemption allowing public offerings of securities up to $75M from any US investors without full SEC registration. Requires SEC qualification (3–6 months), annual and semi-annual reporting.

Regulation D

An SEC exemption allowing private placement of securities to accredited investors without SEC registration. Rule 506(b): no general solicitation. Rule 506(c): general solicitation permitted, mandatory accredited investor verification.

Rollup

A Layer 2 scaling solution that processes transactions off-chain and posts compressed proofs to L1. Optimistic rollups use fraud proofs; ZK rollups use cryptographic validity proofs.

Seed Phrase (Mnemonic)

The 12- or 24-word human-readable backup of a wallet's master key. Anyone with the seed phrase can recover the wallet and all its assets. Never stored digitally; kept in a secure physical location.

Smart Contract

Code deployed on a blockchain that executes automatically when predefined conditions are met. Immutable after deployment. Execution is trustless — no human authorization required.

Solidity

The most widely used programming language for Ethereum smart contracts. Statically typed, compiled to EVM bytecode. Syntax resembles JavaScript/C++.

Stablecoin

A cryptocurrency designed to maintain a stable value relative to a reference asset (typically the US dollar). Types: fully reserved (USDC, USDT), crypto-collateralized (DAI), algorithmic (FRAX).

Tokenomics

The economic design of a token — total supply, distribution, vesting, emission schedule, governance rights, and utility. Well-designed tokenomics sustains the protocol through market cycles; poorly designed tokenomics leads to death spirals.

TVL (Total Value Locked)

The total value of assets deposited in a DeFi protocol, measured in USD. TVL is the primary measure of protocol adoption and trust.

USDC

USD Coin — a fully reserved US dollar stablecoin issued by Circle. Each USDC is backed by $1 in US Treasury bills or bank deposits. The standard stablecoin for US business applications.

Validators

A participant in a Proof of Stake blockchain network that proposes and attests to blocks. Ethereum validators stake 32 ETH. Earning: block rewards + transaction fees + MEV.

Wallet

Software or hardware that manages cryptographic keys allowing users to interact with blockchains. Custodial: the service holds keys. Non-custodial: the user holds keys.

Web3

The third generation of the internet — characterized by user ownership of data and digital assets through blockchain technology, as opposed to Web2 where platforms own user data.

ZK Proof (Zero-Knowledge Proof)

A cryptographic method allowing one party to prove knowledge of information without revealing the information itself. ZK rollups use ZK proofs to prove transaction validity to Ethereum L1 without revealing every transaction detail.