# Flash Loan

> A loan that is borrowed and repaid inside a single blockchain transaction. No collateral needed.

Canonical URL: https://fudfomo.co/glossary/flash-loan
Source: What The Block! Dictionary v1.0 (last updated 2026-04-25), browsable at https://wtb.fudfomo.co.

## Definition

A flash loan lets you borrow a large amount of crypto without putting up collateral, on one strict condition: you must pay it back within the same transaction. If you do not, the entire transaction reverts and it is as if it never happened.

Flash loans are useful for arbitrage and refinancing, but they have also been used in attacks that exploit price oracles or pricing bugs in DeFi protocols.

## Related terms

- [DeFi](https://fudfomo.co/glossary/defi): Decentralised finance. Apps that offer lending, trading, and saving on a blockchain instead of through a bank.
- [Lending Protocol](https://fudfomo.co/glossary/lending-protocol): A DeFi app that lets users deposit crypto to earn interest and others borrow against collateral.
- [Oracle](https://fudfomo.co/glossary/oracle): A service that brings outside information, like prices or sports scores, onto a blockchain.
- [MEV](https://fudfomo.co/glossary/mev): Extra profit that validators or specialised bots can earn by reordering or inserting transactions in a block.

## See the full catalogue

What The Block! covers more than 2,000 plain-English crypto terms, delivered as embeddable hover-state tooltips for crypto exchanges. https://wtb.fudfomo.co