Corn can be considered either a grain or a vegetable, based on when it is harvested. The maturity level of corn at harvest affects both its use at meals and its nutritional value. Corn that is harvested when fully mature and dry is considered a grain. It can be milled into cornmeal and used in such foods as corn tortillas and cornbread. Popcorn is also harvested when mature, and is considered to be a whole grain.
On the other hand, fresh corn (e.g., corn on the cob, frozen corn kernels) is harvested when it is soft and has kernels full of liquid. Fresh corn is considered a starchy vegetable. Its nutrient content differs from dry corn, and it is eaten in different ways -- often on the cob, as a side dish, or mixed with other vegetables.