This is defined as fuel being vaporized (usually due to high temperature) on the tank side of the fuel pump, so that the pump, which is designed to pump liquid, not vapor, will be unable to move fuel to the carburetor, and the car dies. This is most likely to happen after the car has been driven hard, shut down, allowed to heat soak for a while, then restarted and driven off. When the gas in the carburetor has been used up, (typically a block or so), the car will stumble and die. Upon inspection of the carburetor, it will be found to have no fuel. Often a car will begin to show this symptom after the fuel lines from the tank to the pump have aged, and develop a slight porosity. Since this line is under suction, any porosity causes an injection of air, rather than an loss of fuel. Thus it is often not detectable except by the fact that a car which never had vapor lock starts developing the symptom. The cure is to replace
all the rubber hoses which contact fuel with new ones, and be sure they show a SAE rating of "Fuel and Vapor, R9 spec" or equivalent.
since i raised the question as to what it was,, and I got no answers I figured we all could benefit from hearing it.