Negative pressure is a common term when referring to differential pressure. The place I most commonly see it is for isolating rooms with positive[1] or negative

Negative pressure is a common term when referring to differential pressure. The place I most commonly see it is for isolating rooms with positive[1] or negative[2] pressure relative to their surroundings. [1] https://en.wikipedia.org/wiki/Positive_pressure https://en.wikipedia.org/wiki/Positive_pressure [2] https://en.wikipedia.org/wiki/Negative_room_pressure https://en.wikipedia.org/wiki/Negative_room_pressure