Hooks add smart contract functionality to the XRP Ledger: 'layer one' custom code to influence the behaviour and flow of transactions. Hooks are small, efficient pieces of code being defined on an XRPL account, allowing logic to be executed before and/or after XRPL transactions.
The XRP ledger is known and is being appreciated for its transaction throughput, speed and the low fees. Combined with available advanced transaction types like multi sign, escrows, payment channels and even a decentralized exchange (all on ledger, out of the box, without requiring smart contracts) the XRPL has a lot to offer businesses and (creative) developers.