A children's game where one person hides their face (or hides) and then suddenly reveals themselves, saying 'peek-a-boo!' to surprise another person, usually a small child.
From 'bo' (an exclamation) + 'peep' (to look quickly or secretly). Popularized by the nursery rhyme about Little Bo-Peep who lost her sheep, dating back to the 1600s.
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