Flash Loan
An uncollateralized loan that must be borrowed and repaid within a single transaction — impossible in traditional finance, native to DeFi.
A flash loan lets you borrow any amount with zero collateral, on one condition: you must repay it within the same blockchain transaction. If repayment fails, the entire transaction reverts as if it never happened — so the lender can never lose. This is only possible because blockchain transactions are atomic (all-or-nothing).
Legitimate uses include arbitrage, collateral swaps and refinancing without upfront capital. But flash loans also power flash loan attacks — borrowing enormous sums to manipulate a thin oracle price or governance vote, then profiting and repaying in one atomic strike. They’re a genuinely novel financial primitive with a genuinely novel attack surface.