What is fuel cut?

Fuel cut is cessation of fuel delivery and spark generation by the ECU. It is a pre-programmed response designed to save the turbocharger from utter destruction in the event of a catastrophic wastegate malfunction.

Crankbender@DSMTuners: Fuel cut IS NOT due to low of fuel pressure, too small of injectors, high flowing exhaust, high flowing intake, or large turbos. Fuel cut is actually caused by the ECU seeing more air entering the engine than it was originally programmed to use. This likely cooresponds with an injector duty cycle which is unsafe or unattainable. So basically fuel cut is caused by the MAF seeing too much air. Do not ask what too much air is.

Since fuel cut is caused by the ECU seeing too much air we get fuel cut by increasing the air flow through the MAF. 

You can read the answer to How do I prevent fuel cut? in this FAQ.

There is also a thread on DSMTuners Fuel Cut: What is it? How do I fix it? [merged]

Old Links: For more details, read the ECU Primer, specifically the chapter on fuel cut.