A hasty retreat or evacuation, often military or emergency in nature; can also mean a situation where one abandons plans or leaves suddenly.
From the verb phrase 'bug out' meaning to retreat hastily, where 'bug' possibly means to move away quickly (origin uncertain, possibly 1940s military slang).
Military slang often becomes mainstream language—'bugout' entered popular English during WWII and the Korean War when soldiers needed quick words for retreat, now it's used for any panicked evacuation.
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