Difference between general visual inspection and pre-flight check inspection
A GVI is a maintenance procedure that has to be performed by a mechanic qualified to do so, to satisfy a Maintenance Program requirement, and which will require a maintenance release to be signed off.  

A pre-flight inspection is an inspection performed by a pilot in command (or someone delegated by the PIC - like a First Officer, or a mechanic) to satisfy the PIC that the aircraft is safe for flight.

The pre-flight, being a look-over to make sure nothing has fallen off, is dribbling fluid, or is flat, is going to be more superficial than a GVI and usually doesn't involve getting your hands dirty (at airlines it's usually done by the First Officer while in uniform) and normally doesn't involve opening access panels or doors (but could).  Also the pre-flight is a whole-aircraft once-over while a GVI is usually system or zone specific in keeping with its Maintenance Program objectives.