Flash loans are loans that can be taken by anyone without having to put any collateral.

Its possible because they need to be repayed in the same block they are taken.

All of this is ensured by a smart contract, anyone can call it, with the list of actions to do and then repay the loan, if the contract detect that the loan is not fully repayed in the same block, it will refuse the transaction.

Usually platforms allowing flash loans take a fee on top, this is the case for BentoBox : 0.05%.

Flash loans are particularly useful for arbitrage and liquidations. Allowing bots and users to be efficient without the need to have high amount of funds in their wallets.