What does it mean when you smell fumes coming from the air vent in a 2002 passat when the car is stopped?

Depends on the smell. if it smells sweet, like antifreeze, then it is probably a leak in the heater core. This is a small radiator that runs from the main radiator and makes hot air for the heater. If it smells like gasoline, may be a gas leak. Do not drive the car, get it fixed by a professional. If it smells like smoke, it may be an oil leak. get it checked.