Vapor pressure
The portion of atmospheric pressure that is exerted by the moisture in the air (expressed in tenths of an inch of mercury).
Also defined in 2 more sources
The pressure of the vapor above a liquid needed to prevent the liquid evaporating. Vapor pressure is always specified at a specific temperature.
Aviation Maintenance Technician Handbook — Airframe, p. G-38
The amount of pressure needed above a liquid to prevent it from evaporating.
Aviation Maintenance Technician Handbook — Powerplant, p. G-30