Corn may be considered either a vegetable or a starch depending upon variety and usage. Sweet corn is considered a vegetable for culinary purposes, while field corn and popcorn are considered a starch.
Popcorn may be considered a starch rather than a vegetable due to its nutritional profile. Corn meant for being ground into flour or meal is also not considered a vegetable as it is not used for direct human consumption like sweet corn is.
Sweet corn is usually eaten before most of its sugar converts to starch, and is prepared either on the cob or as cooked kernels.