means Corn kernels that burst into fluffy white morsels when heated, eaten as a snack — especially at movies.

from A plain American compound of "pop" (the bursting sound, itself imitative — the word literally sounds like the thing it names) and "corn," the New World grain. The exploding-corn trick is genuinely ancient: Indigenous peoples of the Americas were popping maize for thousands of years before Europeans arrived, the kernels' hard moisture-trapping hulls doing the same steam-pressure magic then as now. The snappy English name itself is a 19th-century coinage, blooming alongside the kernels at fairs and, later, cinema lobbies.