1. The volume of air which flows air gap, 1 through a closed window or door in a given length of time as a result of the difference in air pressure on its opposite faces.
2. In ductwork, air which escapes from a joint, coupling, etc.
3. The undesired leakage or uncontrolled passage of air from a
ventilation system.
4. The flow of uncontrolled air through cracks or openings in an enclosure within a building (such as a HVAC plenum) or through the surfaces which enclose the building.