Boost is what makes Squid so fast. It is an intent-like model which brings transaction times down to less than 20 seconds in all cases.
Boost is a smart contract overlay which allows a provider to optimistically fulfill a transaction immediately after the user completes their transaction on the source chain. The provider is providing a short term loan, which is guaranteed by the pending bridge transaction.
Boost can be used with any Squid feature, including hooks, fees, gas on destination, etc.