What is Flash Loan

A flash loan is an uncollateralised DeFi loan that must be borrowed and repaid within the same blockchain transaction. If the borrower fails to repay the full loan amount plus fee before the transaction completes, the entire transaction is atomically reverted — as if it never happened. This atomic guarantee enables zero-collateral lending: the lender has no default risk because repayment is guaranteed by the blockchain itself. THE MECHANICS OF ATOMICITY Ethereum transactions are atomic: either all steps execute successfully, or none do (complete revert). A flash loan exploits this property: Step 1: Request flash loan of 10M USDC from Aave. Step 2: Use 10M USDC to execute profitable operations (arbitrage, liquidation). Step 3: Repay 10M USDC + 0.09% fee to Aave. If Step 3 fails or funds are insufficient: the entire transaction reverts. Aave never loses its principal — it's returned or the loan never happened. LEGITIMATE FLASH LOAN USE CASES Arbitrage: Borrow large capital to execute arbitrage between DEXs profitably at scale — without needing the capital personally. Self-liquidation: Repay your own DeFi loan before liquidation penalty, using flash loan to source the repayment capital without selling collateral. Collateral swaps: Replace your Aave collateral from ETH to WBTC in one transaction using a flash loan bridge. Position refinancing: Move a leveraged position from one protocol to another in a single atomic step. FAMOUS FLASH LOAN EXPLOITS Flash loans are the weapon of choice for many DeFi attacks because they give attackers unlimited temporary capital: bZx (2020): First major flash loan attack. $350K profit from price oracle manipulation using borrowed capital. Cream Finance (2021): $130M stolen via recursive borrowing using flash loans. Euler Finance (2023): $197M attack using flash loan-enabled donate/liquidate mechanism. Most flash loan "exploits" are actually smart contract vulnerabilities — the flash loan is merely the tool providing capital to exploit the flaw. FLASH LOAN PROVIDERS Aave: The largest flash loan provider. 0.09% fee. Supports ETH, WBTC, USDC, DAI, and dozens of assets. dYdX: Zero-fee flash loans. Uniswap V3: Flash swaps — a related mechanism where tokens can be borrowed temporarily within a swap.

Terms in addition to the Flash Loan

Blockchain

A blockchain is a subset of a distributed database. The Bitcoin inventors originally prototyped the system in 2008. This modern database is made up of separate blocks that are connected together in a chronological chain. Blockchains may be used to store a wide range of data types. It has mostly been utilized as a public ledger for bitcoin transactions to date. A peer-to-peer network comprised of independent nodes uses a consensus process to ensure the blockchain's security and legitimacy. Each node in the network keeps a public and immutable copy of the data.

2 Factor Authentication (2FA)

2 Factor Authentication is a security measure with two layers. It is used by the majority of cryptocurrency exchanges. To log in, you must provide not only a password, but also a code obtained, for example, from the Google authenticator.

Airdrop

An airdrop is a method of distributing coins. End users can typically obtain coins for free or in exchange for doing a small task, such as subscribing to a newsletter, sending a tweet, or inviting others via a personal affiliate link. Cryptocurrency airdrops — the act of depositing cryptocurrency into public crypto wallets — are utilized as a marketing, liquidity creation, and network bootstrapping technique for many different types of blockchain initiatives.

Altcoin

Altcoin - "alternative coin" - is any kind of digital currency other than Bitcoin. Since the launch of Bitcoin, the world's first digital currency, many altcoins (as well as supporting blockchains) have been created. Altcoin digital currencies share many similarities to Bitcoin, but consistently and have significant differences. There are about 20,000 altcoins, and this number is expected to grow significantly in the coming years. Altcoins often develop Bitcoin features. Ethereum, currently the most widely used blockchain, supports digital contracts and separate applications where Bitcoin does not. Altcoins are also often created to cater to the needs of different users. The Litecoin blockchain, for example, can process payments quarterly for the duration of Bitcoin.

Cold Storage

Cold storage is the way to store cryptocurrency offline. The word refers to the use of offline wallets that are not connected to the internet. Cold storage is the most secure way to keep cryptocurrencies since an offline currency becomes less likely to be hacked and stolen. Paper wallets, printed renditions of private keys, and offline hardware and software wallets are all examples of cold storage.