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Web3 security glossary

Short, plain-language definitions of the terms you will meet in a smart-contract audit.

Core terms

TermMeaning
ReentrancyRe-entering a function via an external call before its state is updated, enabling repeated withdrawals.
MEVMaximal Extractable Value: profit a block producer or searcher can extract by reordering, inserting or censoring transactions.
Sandwich attackAn MEV tactic that places one transaction before and one after a victim's trade to profit from the induced price movement.
TWAPTime-Weighted Average Price: an oracle method resistant to single-block price manipulation.
Flash loanAn uncollateralized loan repaid within the same transaction, often used to amplify manipulation.
delegatecallA call that runs another contract's code in the caller's storage context; dangerous if the target is untrusted.
Checks-Effects-InteractionsA pattern: validate inputs, update state, then interact with external contracts.
PDAProgram Derived Address on Solana; must be validated with the correct seeds and bump.
Signer checkOn Solana, verifying an account actually signed the transaction before trusting it.
SWCSmart Contract Weakness Classification, a registry of known weakness types.

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