From AMS Glossary
Water dripping to the ground from trees or other objects that have collected the moisture from drifting fog.
In some instances the dripping is as heavy as light rain, as sometimes occurs among the redwood trees along the coast of northern California. During the foggy but almost rainless summers of California, fog drip prevents an excessive aridity in the coastal forests. As much as 0.05 in. of water, equivalent to a moderate shower, has been collected from a California fog in a single night. From the aerodynamic principles underlying the theory of collection efficiency it is clear that the needlelike leaves of conifers are better adapted to the removal of droplets from drifting fog than are the broad leaves of most deciduous trees. This characteristic may have been crucial in the evolutionary development of the redwoods in the limited areas wherein they thrive. Man-made fog-water collectors have been constructed in western Chile that utilize fog drip to provide water to the local population.