An evacuation happens when people are removed from or leave a dangerous place. An approaching hurricane sometimes results in the evacuation of islands and coastal towns.
A fire drill or bomb threat can cause the evacuation of a school building, and during World War II there were frequent evacuations of buildings and areas of cities including London, when people hurried into shelters. Another meaning of evacuation is the emptying of something, whether a container or a human body. This relates to the word's original meaning, "discharge of blood from the body," from the Latin evacuare, "to empty."