A pattern where an external call re-enters a contract before an earlier operation has finished.
A contract can call another contract, which calls back before the first operation finishes updating state. Reentrancy becomes a vulnerability when this interruption breaks accounting or other assumptions. Developers use careful state updates and suitable guards so callbacks cannot act on information that should have changed.
IN THE WILD
The withdrawal callback calls back into withdrawal before the first call updates the balance; that second call sees the old accounting.
A relay-policy mechanism for replacing an eligible pending transaction with a higher-fee transaction.
RBF is often the reason a Bitcoinwallet offers 'bump fee' when a payment is waiting. Replacement depends on node policy and the replacement transaction meeting its requirements. It changes a pending transaction, not an already accepted historical payment, and offering a higher fee still doesn't guarantee immediate inclusion.
IN THE WILD
'My transfer's taking ages.' You use your wallet's fee-bump option to submit an eligible replacement while the payment is still pending.
Reusing a valid authorization where it should no longer apply or should never have applied.
A signature can be cryptographically valid but inappropriate for a second action or another network. Systems use nonces, deadlines and signing domains to restrict reuse. Ethereumtransaction chain IDs provide one kind of network binding; other signed messages need their own suitable replay protection.
IN THE WILD
"This authorization already ran once. Without recording its consumed nonce, the system accepts the same signature again."
An execution failure that rolls back changes made by the affected contract call.
A revert is a contract saying the requested action can't complete under its rules. It might mean a swap's minimum output wasn't met or a caller lacked permission. If the whole included transaction reverts, its execution changes are rolled back, but consumed gas still costs money and the sender's transaction nonce advances.
IN THE WILD
“My swap failed and I still paid gas.” The minimum-output check triggered a revert after the network had already done execution work.
A scaling system that executes transactions separately and publishes required data and commitments to a base chain.
Instead of asking the base chain to execute every user action individually, a rollup handles transactions in batches. Its proof or dispute mechanism links the resulting state to settlement. Publishing the required data distinguishes rollups from designs relying on offchain data availability, even when both use validity proofs.
IN THE WILD
The rollup collects many transfers into one batch and publishes the required data, rather than asking Ethereum to execute each transfer individually.
A wallet often needs an RPC endpoint to read balances, obtain chain data or submit transactions. A provider makes that connection easier than running a node yourself. It also becomes a dependency for availability, the information returned and query privacy; an unavailable endpoint can make a working chain look unresponsive.
IN THE WILD
"The explorer sees my transaction, but my wallet's RPC endpoint is not returning current data."
One hundred millionth of a bitcoin, commonly shortened to sat.
Sats let you discuss small Bitcoin amounts without counting a row of decimal places. There are 100 million satoshis in one BTC. Bitcoin's normal onchain amounts use whole satoshis, while Lightning can account for smaller millisatoshi amounts inside channels. The unit tells you quantity, not purchasing power.
IN THE WILD
'That costs 5,000 sats.' The price is 0.00005 BTC, written in a unit that's easier to read.
BitcoinTaproot uses the Schnorr scheme specified in BIP-340. Its mathematics allows useful combinations in suitable protocols, but aggregation needs a correctly designed protocol around it. In a regular Taproot key-path spend, the visible result is a signature nodes can verify against the required key.
IN THE WILD
Inspect a BitcoinTaproot key-path spend: the required authorization is supplied through a BIP-340 Schnorr signature.
Recovery words used by many wallets to derive the keys that control an account.
The words are recovery material, not a password for a website. Someone obtaining the required recovery material can usually recreate the signing keys. A separate passphrase or another scheme can add requirements. Restoring also needs compatible wallet conventions, so the words do not make every app interchangeable.
IN THE WILD
"I can restore with my private recovery backup. That support DM asking me to send the words is a different story."
A Bitcoin upgrade that separates witness data, such as signatures, from the traditional transaction serialization.
SegWit changed transaction identification and block-capacity accounting. For relevant spends, keeping witness data out of the traditional transaction IDaddresses important forms of transaction malleability. You'll meet it in wallet address formats and fee discussions, but the upgrade doesn't make every transaction smaller or eliminate every possible malleability issue.
IN THE WILD
A SegWit transaction stores its signature data in the witness section; its traditional transaction ID excludes that witness data.
The daily pick rotates automatically. Our initial collection was published on October 9, 2026. New words join on their publication date. Every concept includes a reference.