means A short, sharp burst of sound — or the quick action that makes it — and by extension a sudden brief appearance or movement (as in to pop up or pop in).

from Pop is imitative — what linguists call onomatopoeia, a word born to mimic the very noise it names: the little burst of a bursting thing. It's been in English since the Middle Ages, and like its sound-twin cousins clap, snap, and bang, it didn't descend from some ancient root so much as escape from the mouth directly. The fizzy drink sense ('soda pop') arrived in the early 19th century, named for the satisfying pop of the cork.