Fallout/ˈfɔːlaʊt/ Definition 1 of 3Pro Tip 1/3Technical Term Used specifically in discussions about nuclear events or their impact. The fallout from the test detonation affected nearby wildlife. Pro Tip 2/3Literal Component Fallout literally falls out of the sky after a nuclear explosion. Cities downwind from the blast may experience fallout within hours. Pro Tip 3/3Emergency Context Commonly used in safety procedures or emergency broadcasts. Residents should seek a fallout shelter immediately following an explosion.