Flash Loan

Flash loans are a DeFi primitive that allows borrowing any amount of liquidity without collateral, provided the loan is repaid within the same transaction block. They're used for arbitrage, collateral swaps, and self-liquidation. They are also the primary tool used in many DeFi exploits — attackers borrow large sums to manipulate oracle prices, drain liquidity pools, or execute complex attack sequences, then repay within the same transaction, keeping the profit.