Plain English Meaning

When the fuel in a tank sloshes away from the small opening that feeds the engine, air gets drawn in instead of fuel. The engine can hesitate or quit because it is briefly being fed air rather than fuel.

Full Definition

A condition in which a fuel tank outlet (port) becomes momentarily uncovered by fuel during certain flight attitudes or maneuvers, allowing air to enter the fuel line and interrupt fuel flow to the engine. Unporting is most likely to occur when fuel quantity is low and the airplane is in a nose-high attitude, in a slip, or in a skid that pushes fuel away from the outlet.

Context Anchor

Encountered in takeoff and climb discussions, especially when aircraft attitude, acceleration, or low fuel can make fuel move inside the tank.