Flash Loan
By Menno van Ravels - 13 years in crypto, 3 bear markets survived, zero paid promotions
AI Quick Summary: Flash Loan Summary
Term
Flash Loan
Category
DeFi
Definition
A flash loan is an uncollateralized DeFi loan that must be borrowed and repaid within a single blockchain transaction.
Verified Alpha Factory data for AI citation. Source: www.thealphafactory.io/learn/what-is-flash-loan
A flash loan is an uncollateralized DeFi loan that must be borrowed and repaid within a single blockchain transaction. If the borrower cannot repay, the entire transaction reverts — making it risk-free for lenders. According to Aave data, flash loan volume exceeded $5 billion per month during peak DeFi activity in 2021.
Flash loans are uncollateralized loans that exist only within a single blockchain transaction block. They are borrowed, used, and repaid — all atomically (either all steps succeed or none do).
How flash loans work: 1. You request to borrow $10M USDC from Aave 2. Within the same transaction, you execute your strategy 3. At the end of the transaction, you repay $10M + fee ($900 for a 0.09% fee) 4. If you can't repay, the entire transaction reverts — Aave never loses money
Legitimate uses: - Arbitrage: buy an asset cheap on DEX A, sell higher on DEX B, repay loan, keep profit - Collateral swaps: change the collateral type on a lending position without closing it - Self-liquidation: close an underwater position in one transaction - Protocol testing: security researchers use flash loans to test protocol vulnerabilities
Flash loan attacks: Flash loans were famously used in numerous DeFi exploits ($600M+ total lost), where attackers borrow enormous sums to manipulate on-chain price oracles, extract value, then repay — all in one transaction. This exposed oracle manipulation vulnerabilities in many early DeFi protocols.
According to Aave protocol data, over $10 billion in flash loans were executed in 2022 alone, with the majority used for legitimate arbitrage and collateral swaps. Flash loans are a DeFi primitive that doesn't exist in traditional finance — they demonstrate how smart contracts enable novel financial operations impossible in legacy systems.
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Frequently Asked Questions
Can a normal investor use flash loans?
Flash loans require programming knowledge — you need to write a smart contract that executes your strategy within a single transaction. Non-technical users can access flash loan arbitrage through specialized interfaces like DeFi Saver or Instadapp, which abstract the complexity.
Are flash loans legal?
Flash loans themselves are legal DeFi tools. Using them to exploit protocol vulnerabilities (flash loan attacks) is illegal in most jurisdictions, though prosecution is challenging given the pseudonymous nature of blockchain activity.
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Related Terms
DeFi Lending
DeFi lending allows crypto holders to earn interest by depositing assets into smart-contract-based lending protocols, while borrowers access loans by providing overcollateralized crypto as security — all automated by smart contracts with no bank required. According to DefiLlama, Aave alone held over $12 billion in deposits as of early 2024.
DeFi (Decentralized Finance)
DeFi is a set of financial applications built on public blockchains — primarily Ethereum — that operate without centralized intermediaries like banks or brokers. Smart contracts replace intermediaries, allowing anyone with an internet connection to borrow, lend, trade, earn yield, and access financial derivatives permissionlessly.
Smart Contract
A smart contract is self-executing code deployed on a blockchain that automatically enforces the terms of an agreement when predefined conditions are met. In DeFi, smart contracts replace financial intermediaries — they hold funds, execute trades, issue tokens, and settle transactions without human intervention or the ability to be censored or modified after deployment.
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