The surplus water that is left in trees and other overhanging plants after a previous rain shower. Even after the rain itself has stopped falling, the precipital fallout still lingers, much like the radioactive fallout of a nuclear explosion.
Zack: Hey Devin! Why are you soaking wet?
Devin: You know that storm we had yesterday? I was just hit by some precipital fallout when I walked under those trees over there.