Integrated Water Vapour
Integrated Water Vapour (IVV) is the total amount of water vapor present in a vertical atmospheric column. Considering the density of liquid water, the IWV expressed in kg/m2 is equivalent to the Total Precipitable Water (TPW) expressed in mm of liquid water. Strictly speaking, however, not all the water vapor is actually precipitable.
Sources
WMO. Details for Variable: Integrated Water Vapor (IWV) [Internet]. WMO OSCAR. 2021 [cited 2021 Aug 17]. Available from: https://space.oscar.wmo.int/variables/view/integrated_water_vapor_iwv