Blockchain and Wallet Glossary: From Seed Phrase to Rollup

Blockchain, node, gas, L2, rollup, seed phrase, approval, drainer: crypto's technical terms explained simply, with what they mean for you.

Basics · Débutant · 14 min read · Publié le October 13, 2026

The essentials

The blockchain itself

Blockchain: a shared ledger, copied by thousands of computers, where transactions are grouped into blocks linked to one another. See blockchain explained.
Block: a packet of transactions validated together. About every 10 minutes on Bitcoin, every 12 seconds on Ethereum.
Hash: the unique digital fingerprint of a piece of data. Change a single comma and the whole hash changes. The "tx hash" is a transaction's identifier.
Node: a computer that keeps a copy of the blockchain and checks the rules. A full node verifies everything; a light node keeps only the essentials.
Miner / validator: the one who produces blocks. Miner in Proof of Work, validator in Proof of Stake.
Consensus: the rule that lets all nodes agree on the same history.
Proof of Work (PoW): miners spend electricity to solve a calculation; this is Bitcoin's model. Hashrate: the network's total computing power.
Proof of Stake (PoS): validators lock up ("stake") tokens as collateral; this is Ethereum's model since 2022. See PoW vs PoS.
Slashing: the penalty for a validator who cheats or misbehaves: part of their stake is destroyed.
Finality: the moment when a transaction can no longer be reversed.
Mempool: the waiting room for transactions not yet included in a block.
Nonce: on Ethereum, the sequence number of your transactions (0, 1, 2...). A transaction stuck with one nonce blocks the ones that follow.
Halving: the halving of Bitcoin miners' reward, every 210,000 blocks (about 4 years). See cycles and halving.
UTXO: Bitcoin's model, where your balance is a sum of unspent "coins." Ethereum uses an account model.
Fork: a change of the rules. Soft fork: compatible with the old software. Hard fork: incompatible; if part of the network refuses, the chain splits in two.
51% attack: an actor controlling the majority of computing power or stake can reorganize the recent history.
Mainnet / testnet / devnet: the real network / a test network where tokens have no value / a development network. A faucet hands out free test tokens.
TPS: transactions per second, a throughput measure often inflated by marketing.
Block explorer: the site that displays everything happening on a chain (Etherscan, Solscan, mempool.space). See reading an explorer.
Oracle: the service that brings external data (a price, a result) to the blockchain. See oracles.

Units and fees

Gas: the fuel of a transaction on Ethereum and EVM chains. The busier the network, the more expensive gas is.
Gwei: one billionth of an ETH (10⁻⁹). It's the unit in which gas prices are read.
Wei: the smallest unit of ETH (10⁻¹⁸).
Satoshi (sat): the smallest unit of bitcoin, 0.00000001 BTC.
Lamport: the smallest unit of SOL (10⁻⁹).
Base fee / priority fee: on Ethereum, the base fee is burned (destroyed); the priority fee ("tip") goes to the validator to get included faster.
Gas limit: the cap on gas that a transaction agrees to consume.
Native token: the token that pays the network's fees (BTC, ETH, SOL...). Without it, you can't move your other tokens.

Layers and networks

Layer 1 (L1): a main blockchain (Bitcoin, Ethereum, Solana).
Layer 2 (L2): a network built on top of an L1 to be faster and cheaper, relying on it for security (Base, Arbitrum, Optimism). See Base, Arbitrum, Optimism.
Rollup: an L2 that bundles many transactions and publishes the result on the L1. Optimistic rollup: transactions are assumed valid unless challenged (native withdrawal to the L1 is often long, about 7 days). ZK rollup: each batch comes with a mathematical proof. See optimistic vs ZK rollups.
Sequencer: the operator that orders an L2's transactions.
Data availability (DA): the guarantee that an L2's data is published and accessible. Blobs: the cheap data space added to Ethereum in 2024 for rollups.
Sidechain: a parallel chain with its own security (less protected than a rollup).
Appchain: a blockchain dedicated to a single application.
Bridge: a way to move assets from one chain to another; historically one of hackers' favorite targets. See bridges.
Wrapped token: the "wrapped" version of an asset on another chain (WBTC = bitcoin represented on Ethereum). WETH: ETH wrapped in the ERC-20 format.
EVM: Ethereum's virtual machine. An "EVM-compatible" chain accepts the same wallets and the same 0x addresses. Solana has its own machine (SVM).

Contracts and tokens

Smart contract: a program deployed on the blockchain, which runs by itself according to its code.
dApp: a decentralized application, a web interface that talks to smart contracts.
Verified contract: a contract whose source code is published and verified on the explorer. An unverified contract is a warning sign.
CA (Contract Address): the address of a token's contract. It, not the name or the logo, identifies the real token.
Token standards: ERC-20 (classic token on EVM), ERC-721 (unique NFT), ERC-1155 (multi-token), SPL (Solana tokens), BRC-20 (tokens on Bitcoin via inscriptions). See coins, tokens and standards.
Coin vs token: a coin is native to its chain (BTC, ETH); a token is issued by a contract on an existing chain.
Burn: sending tokens to an address whose key nobody has, to destroy them. Burn address: for example 0x000...dEaD.
RPC: the access point that connects your wallet to the blockchain. See private mempool and protected RPCs.

Wallets and keys

Wallet: the app or device that holds your keys and signs your transactions. Your crypto is on the blockchain, not "in" the wallet.
Private key: the secret that proves you're the owner. Whoever has it controls the funds.
Public key / address: what you share to receive. An EVM address starts with 0x, a modern Bitcoin address with bc1.
Seed phrase (recovery phrase): 12 or 24 words (BIP39 standard) that let you recreate all your keys. Never type it on a website, never photograph it. See private key and seed phrase.
Passphrase (25th word): a password added to the seed that creates hidden wallets. See the BIP39 passphrase.
Derivation path: the "route" that turns a seed into addresses. Two wallets that don't use the same path won't show the same addresses.
xpub: the extended public key, which lets you see all the addresses of a Bitcoin wallet without being able to spend.
Custodial / non-custodial: the platform keeps the keys (exchange) / you keep your keys (self-custody). "Not your keys, not your coins."
Hot wallet / cold wallet: a wallet connected to the Internet / keys kept offline. See hot vs cold.
Hardware wallet: a physical device that holds the key and signs without exposing it to the computer. Air-gap: no cable or Bluetooth, signing goes through a QR code. See setting up a hardware wallet.
Secure element: a secure chip that protects the key against physical extraction.
Multisig: a wallet requiring several signatures (e.g. 2 of 3). See multisig and Safe.
MPC wallet: the key is split into pieces spread across several devices or servers.
Smart wallet / account abstraction: a wallet that is itself a smart contract: social recovery, fees paid by a third party (paymaster), session keys, login by passkey. See account abstraction.
ENS / domain names: a readable name that replaces an address (vitalik.eth). Convenient, but always check the real address behind it.

Signatures and security

Signature: your cryptographic approval of a transaction or message. Signing can be enough to lose funds, even with no visible transaction.
Approval (allowance): the permission given to a contract to spend a token on your behalf. An unlimited approval stays active until you revoke it. See revoking approvals.
Revoke: removing an approval (with Revoke.cash or the explorer's tool).
Permit / Permit2: approvals given by a simple off-chain signature. Convenient, and heavily used by drainers.
Blind signing: signing without being able to read what the transaction contains. Clear signing: the wallet displays in plain language what you're signing.
Drainer: a fake site or script that empties your wallet after a signature. See phishing and drainers.
Address poisoning: a scammer sends you a transaction from an address that looks like a contact's, hoping you'll copy it from your history.
Dust attack: sending micro-amounts to track or trap a wallet.
Checksum: on EVM, the mix of uppercase and lowercase letters in an address serves as an error check.
Stuck transaction / speed up / cancel: a transaction with too little fee can stay pending; the wallet offers to speed it up or cancel it by paying more.