(1) The rainfall useful for meeting plant water requirements. This does not include water percolating down to aquifers, or surface runoff of water (cf. definition (2)!)
(2) The difference between precipitation and evapotranspiration, i.e. the water percolating to aquifers or surface runoff (cf. definition (1)!).
(3) The amount of rainfall after subtracting the fraction that has been directly evaporated from the canopy surface without reaching the soil surface (as in coniferous forests).