“Fuel cut” is a safety feature that is intended to protect your motor from too much turbo boost. The factory ECU keeps track of the pressure inside the intake manifold, and if that pressure goes above a certain level (around 18-19 psi on most cars), the ECU will turn off the fuel injectors. It’s just like shutting off the motor momentarily.
A “fuel cut defenser” or “FCD” is a device that overrides this saftey feature and will let you either raise the limit that fuel cut is set, or will eliminate fuel cut altogether.