[EN 12792:2003, 271]:ability of an air transfer device to prevent the air flow from reversing when the pressure difference Δp across it is inverted.

[ASHRAE Standard 62.1]:occupancy of a dwelling unit or sleeping unit for more than 30 days.

[EN 12792:2003, 272]:air terminal device designed to achieve the maximum conversion from static pressure energy to dynamic energy and thus produces a maximum throw due to minimum entrainment.