Check Engine Light on, FUEL TRIM reading

[yellowboxster]

Hello,

My check engine light is on and I went to my Porsche Mechanic and he checked it and said it was the fuel trim. He says it can be anything from O2 sensor to vacuum leaks. What is fuel trim exactly? and what can it be? I have a 2002 Boxster 2.7 90km. Also sometimes right before redline it feels like the fuel cuts out like the engine shuts off for a split second. Does this have anything to do with the "fuel trim"?

Thanks in advance for your help.