This glossary covers only terms tied directly to custody, signing and theft; trading and market terms are left out. The standards and official documentation cited in the entries are linked and were checked in October 2026. Standards and products change, so go by what each link says now.
Keys and seed phrases
Private key
A randomly generated 256-bit number. Whoever holds it can sign for the matching address and move the coins. The wallet generates it locally; it is not on-chain and not registered on anyone's server, so if you lose it nobody can retrieve it for you, and if it leaks it cannot be changed, only replaced with a new one. You prove that you hold a private key by signing, without ever showing the key; anyone who asks for your private key to “verify” something is running a scam. See the section on what a private key is in Private Key vs Seed Phrase.
Public key
A number computed one-way from the private key, safe to make public. Others use it to verify that a transaction's signature really came from the matching private key; working back from the public key to the private key is not feasible with existing computing power. Everyday transfers use the address, a shorter string obtained by hashing the public key. The derivation is walked through in the section of the same guide on how private key, public key and address are derived.
Address
The string you give out to receive funds, obtained from the public key by hashing and encoding; sharing it does not put assets at risk. Formats differ by chain: Ethereum and EVM chains such as BNB Chain, Polygon and Arbitrum share one 0x-prefixed format, and the same address has a separate ledger on each of those chains; Tron uses a different format starting with T, and Bitcoin another again. So before a transfer, check the full address character by character and confirm that both sides have the same chain selected; see Sent USDT to the Wrong Network? What to Do.
Mnemonic
The name BIP-39 gives to what this site calls a seed phrase: a set of words, usually 12 or 24, that encodes a random number. Every private key in the wallet is computed from it, so it amounts to the whole wallet: if the device breaks or is lost, it restores the wallet on a new device, and anyone else who gets hold of it can move everything. It must have an offline backup; where to keep one is covered in How to Store Your Seed Phrase Safely.
Seed phrase
The everyday name for the mnemonic. Wallet interfaces also call it a recovery phrase or a wallet backup; they all mean the same thing. Strictly speaking, the seed is the 512-bit number computed from the mnemonic and the mnemonic is its easy-to-copy form, but ordinary usage does not separate the two. For how to look after it, see the Mnemonic entry.
BIP-39
The standard that specifies how a random number becomes a seed phrase. It uses a fixed list of 2,048 words, each encoding 11 bits, with checksum bits at the end, so a made-up string of words will usually fail the checksum; the seed phrase, together with an optional passphrase, is then turned into a 512-bit seed. The text is at BIP-39, and it is explained step by step in the BIP-39 section of Private Key vs Seed Phrase.
BIP-32
The standard that specifies how a whole tree of private keys is derived level by level from one seed; wallets built this way are called HD (hierarchical deterministic) wallets. Because of it a single seed phrase can manage many addresses with one backup, and adding an address needs no new backup. The text is at BIP-32; how the three standards divide the work is in Which part BIP-39, BIP-32 and BIP-44 each cover.
BIP-44
Sets a common path layout on top of the BIP-32 key tree, m / purpose' / coin_type' / account' / change / address_index, so that different wallets number coins, accounts and addresses the same way. Ethereum's familiar m/44'/60'/0'/0/0 follows it. The text is at BIP-44.
Derivation path
The route from the seed to one specific private key, written in a form like m/44'/60'/0'/0/0. The same seed phrase produces different addresses along different paths, so if a balance is missing after you import a seed phrase into another wallet, first check whether the two wallets use the same derivation path; the coins are most likely not lost. The path itself does not need to be kept secret. See the section on addresses that differ after switching wallets.
Passphrase (the 25th word)
An optional extra secret in BIP-39 that goes into the seed calculation together with the seed phrase. The same seed phrase with a different passphrase gives an entirely different wallet; every passphrase is valid, so a wrong one raises no error and simply opens an empty wallet. According to Trezor, the device does not store it and a forgotten one cannot be recovered, so back it up just as you do the seed phrase and keep the two apart. It is a different thing from the wallet app's unlock password, which can be reset by importing the seed phrase again. See the passphrase section of How to Store Your Seed Phrase Safely.
Shamir backup (SLIP-39)
Splits one backup into N shares, any M of which are needed to recover; no combination of fewer than M shares can restore it. The corresponding standard is SLIP-39, published by SatoshiLabs, and it is not interchangeable with a BIP-39 seed phrase. According to Trezor, hardware wallets that support this kind of backup include Trezor, OneKey and Keystone; for specific models go by each vendor's official page. A split backup sets how many shares are needed to recover, whereas multisig sets how many keys are needed to spend. See the split backup section of How to Store Your Seed Phrase Safely.
Wallet types and hardware
Hot wallet
A wallet in which the device holding the private key is online when it signs; wallet apps on a phone and browser extension wallets belong here. The convenience has a price: malware on that device has a chance of reaching the private key. Keep in it only an amount you could lose without it affecting your life. See the definition section of Cold Wallet vs Hot Wallet.
Cold wallet
A wallet in which the device holding the private key is offline when it signs. A hardware wallet in normal use belongs here, even when plugged into an online computer, because it is the computer that is online and not the device holding the key. One consequence: once a private key or seed phrase has appeared on an online device, treat it as hot. A cold wallet protects against the online side; it does not protect against a backup that is lost or found by someone else, or against you confirming a wrong transaction on the device. See the five situations covered in the same guide.
Hardware wallet
A small device built to hold private keys: the keys are generated and stored inside it, a transaction is passed in, confirmed on the device and signed there, and only the signature comes out. Models differ considerably in whether they have a secure element, how they connect to a computer or phone, and which backup methods they support; go by the official spec pages, summarized in Hardware Wallet Comparison. Buy only from the manufacturer or an authorized seller, and do not use a device that arrives with a ready-made seed phrase in the box.
Secure element
A separate chip designed to resist physical extraction, which hardware wallets use to protect PIN verification and keys. Whether a model has one, and which one, varies: according to Trezor's documentation, the Safe 3, Safe 5 and Safe 7 have a secure element and the Model One and Model T do not. A secure element affects how hard it is to read the private key out of a device that has fallen into someone else's hands; it does nothing about you confirming a wrong transaction on the screen. Chips and certification levels by model are in Hardware Wallet Comparison.
Air gap
No cable, Bluetooth or Wi-Fi between the signing device and the online device; unsigned transactions and signed results travel back and forth by QR code or memory card. Malware on the online side then has no direct channel to the signing device. What it cannot stop is the same as with any other hardware wallet: a transaction whose content is the problem, confirmed without reading the device screen properly. For a model in the comparison table that uses only QR codes and microSD, see Keystone 3 Pro.
Paper wallet
Keeping a private key or seed phrase written or printed on paper. Paper is offline; its weaknesses are fire, water, loss and being seen. The more common practice now is to hand-copy the seed phrase generated by a hardware wallet onto paper or a metal plate as the backup. Generating a private key with a web tool and printing it is not advised, because the key has then already appeared on an online computer and a printer. See the paper section of How to Store Your Seed Phrase Safely.
Multisig
A wallet tied to n keys in which a transaction needs signatures from at least m of them, written m-of-n, for example 2-of-3. If one key is lost, the wallet still works as long as m of the remaining n − 1 are available and the multisig configuration was backed up with each key; if one is stolen, the thief cannot reach m and cannot move anything. The cost is collecting signatures every time funds move, and on Ethereum multisig is implemented with smart contracts, which adds the risk of contract code. See the multisig and social recovery section of How to Store Your Seed Phrase Safely.
Social recovery wallet
A smart contract wallet design: day to day a single signing key approves transactions, and you also appoint several guardians. If the key is lost, a majority of the guardians can cooperate to replace the account's signing key, while the account and its assets stay where they are. Guardians can be your own other devices, friends and family, or institutions. The definition comes from Vitalik Buterin's Why we need wide adoption of social recovery wallets; the trade-offs against multisig are in the multisig and social recovery section.
Account abstraction (ERC-4337)
Lets smart contract code set the rules by which an account validates transactions, where an ordinary account accepts only the signature of one private key. ERC-4337 is one way of doing this on Ethereum; according to the standard, it needs no change to the consensus layer: users send UserOperation objects to a separate mempool, and bundlers package them into transactions for inclusion on-chain. Wallet features such as social recovery and shared control by several keys are built on these contract accounts.
Approvals and signatures
Token approval
Through the token contract's approve function you allow a contract address to spend up to a set amount of that token from your account; swapping on a DEX or depositing into a lending protocol usually begins with this step. Approvals are recorded per token and per chain and do not expire. If the amount is unlimited and the approved contract goes wrong, your entire balance of that token can be taken. See the section on why unlimited approvals are dangerous in How to Check and Revoke Token Approvals.
setApprovalForAll
The approval switch in NFT contracts. According to the ERC-721 text, it enables or disables approval for a third party (an operator) to manage all of your assets in that contract. It is either on or off, with no amount; once signed, the operator can transfer every item you hold under that NFT contract. Revoking means setting it back to false; see How to revoke an approval.
Permit signature (EIP-2612)
An extension to ERC-20 in which an approval is made by signing an off-chain message, with no approve transaction; the message names the spender, the amount and a deadline. The standard is EIP-2612. The approval takes effect only when the party holding the signature submits it on-chain; until then it appears in neither your transaction history nor your approval list. According to Revoke.cash, you can try to cancel a signature that has not been submitted yet from its Signatures tab, and revoke one already in effect the usual way. See Can a suspicious Permit signature still be cancelled?
Permit2
An approval contract built by the Uniswap team, with two layers: you first give the Permit2 contract itself an on-chain approval, and Permit2 then hands allowances on to individual apps, each with an expiry time. When reviewing approvals, check both layers; see Permit2 has two layers of approval.
Revoke.cash
A website for viewing and revoking token approvals. Enter an address and it lists the approvals that address has given on each chain, with no wallet connection needed; only revoking requires connecting the wallet, signing and paying gas. Open it by typing the domain yourself or from a bookmark, not from search ads or links in direct messages, which is how fake revoke tools draw people in. How to use it is in the Revoke.cash section of How to Check and Revoke Token Approvals.
Etherscan (block explorer)
A website for looking up on-chain data on Ethereum mainnet: enter an address to see its balance and every transaction, or a transaction hash to see who sent it, to whom, and whether it succeeded. Its built-in Token Approval Checker shows approvals. Block explorers are separate for each chain: BNB Chain has BscScan and Polygon has Polygonscan. Looking things up in an explorer needs no wallet connection and triggers no transaction. See Etherscan's Token Approval Checker.
Common attacks
Phishing
Impersonating an official website, a support agent, an airdrop campaign or a wallet pop-up to get you to hand over your seed phrase, password or verification code, or to sign an approval yourself. It breaks no cryptography; it relies on people misreading and rushing. Two rules cover most of it: never enter the seed phrase in any web page or tell it to anyone, and never confirm a wallet pop-up you do not understand. How to recognize the common methods is in the guide to crypto phishing scams.
Address poisoning
A scammer generates a fake address whose first and last characters match one you use often, then sends you a zero-value transfer to plant that address in your transaction history, hoping you will copy it from there next time. According to MetaMask's help center, the transfer itself causes no loss; the loss comes when you send coins to the fake address, and what is sent cannot be recovered. The defense is to never copy addresses from transaction history, to check the full address character by character, and to save the addresses you use often in the address book. How it differs from an unknown token is explained in Why Did a Random Token Appear in My Wallet?
Dusting attack
Sending a tiny amount of coins to a large number of addresses, then watching which other addresses' funds those amounts are later spent with, in order to infer which addresses belong to the same person. It steals nothing directly; the aim is to tie addresses to people ahead of targeted fraud. If a small transfer arrives out of nowhere, leave it where it is. It is a different thing from address poisoning and from fake airdrop tokens that carry a URL; the differences are set out in Why Did a Random Token Appear in My Wallet?
Airdrop
A project distributing tokens directly to users' addresses. Scams borrow the name: an unknown token is sent to your address, and its name or an accompanying website tells you to “claim” or “swap” it, when the real aim is to have you sign an approval for your real tokens or enter your seed phrase. A token you did not buy or swap for yourself can simply be left alone; see Why Did a Random Token Appear in My Wallet?
Clipper (clipboard hijacking)
Malware that watches the clipboard and, when you copy a wallet address, silently replaces it with the attacker's, so that what you paste is no longer what you copied. The defense is to check the full address character by character after pasting, and to send a small amount first when paying a new address. If you find that a pasted address has been altered, stop using that device for wallet operations and treat it as compromised; see Seed Phrase or Private Key Leaked? What to Do.
SIM swap
An attacker impersonates you and gets the carrier to reissue or transfer your phone number to a SIM card they hold, after which SMS codes sent to that number reach them. It targets accounts that use SMS for two-factor authentication; the answer is to replace SMS with an authenticator app or a passkey. Published case figures and their source are in Is SMS 2FA Safe? Authenticator vs Passkey.
Account security and other terms
Two-factor authentication (2FA)
A second check at login on top of the password. Exchange accounts commonly offer four kinds: SMS codes, time-based codes from an authenticator app, hardware security keys and passkeys. Their weaknesses differ widely, so which kind you turn on matters more than whether one is on. See the section on the four kinds of two-factor authentication in Is SMS 2FA Safe?
Passkey
A credential that lets you sign in with the device's screen lock (fingerprint, face or unlock code) in place of a password. As the FIDO Alliance defines it, a passkey is a FIDO cryptographic credential tied to an account on a website or application, and it is phishing-resistant by design: if the domain does not match, the device will not sign. How to set one up and what to watch for is in What a passkey is and how to set one up.
Hardware security key (such as a YubiKey)
A separate physical key that you plug in or hold against the device and touch when signing in. No code is typed at any point, so a phishing site has nothing to pass on to the real one. It uses the same FIDO standards as passkeys. Keep a spare, because if the only key is lost you are left with the platform's account recovery process. See Why a hardware security key stops phishing sites.
Withdrawal allowlist
Withdrawal allowlist (labeled “whitelist” on many exchanges) is an exchange account setting: once it is on, coins can be withdrawn only to addresses registered and verified in advance, and withdrawals to any other address are refused. It guards against the step where someone who has got into your account simply withdraws to an address of their own, and it gives you time to notice and act. Where the setting lives, and whether a newly added address has a waiting period, differs by platform; go by the platform's security settings page. Whether to turn it on is answered in the FAQ.
Proof of reserves
A public demonstration by an exchange that the assets it holds are no less than the balances it owes its users. A common method is to build all user balances into a Merkle tree and publish the root, so that users can verify their own balance was included, and then to compare against the balances of the platform's published on-chain addresses. It reflects a single point in time and leaves out the platform's other liabilities, so it is no guarantee that coins kept on an exchange are safe. For the difference between an exchange balance and holding your own private keys, see the custodial vs non-custodial section of 8 Types of Crypto Wallets and Where Keys Live.
Stablecoin
A token whose price is pegged to a fiat currency, usually the US dollar; USDT and USDC are two common ones. The same stablecoin is issued on several chains, each with its own separate contract, and picking the wrong chain for a transfer is a common mishap; what to do about it is in Sent USDT to the Wrong Network? What to Do. Its risk lies outside the wallet: whether it can always be redeemed at face value depends on the issuer's reserves and its own terms.