A Fuel Cut is when fuel to the motor is shut off completely.

This is usually done as part of a Rev Limiter, Launch Control or Boost Cut routine. Fuel Cut Rev Limiters are thought to be somewhat scary, as the engine may run lean from lack of fuel.

Spark Cut is not performed by the stock ECU, but many aftermarket ignitions use it. Spark Cut Rev Limiters are thought to be somewhat less harsh.