But yes if people get hungry enough, field corn easily qualifies as actual food.
Sweet Corn: For Fresh Eating and therefore harvested with a high moisture content which hurts preservation without freezing and total yield.
Dimple is a Field corn, harvested later resulting in a dryer product, lasts longer and has a higher yield.
Flint Corn: Mostly decorative as it looks cool, but again still edible after grinding.
Heirloom: lots of shapes and sizes but significantly lower yield.
Popcorn: A tiny slice of the market but pops when heated.
Corn is amazing. My favorite use of it is for alcohol though.
(Corn doesn't need special processing to be edible, but it does need special processing if you want to avoid dying from nutritional deficiency when having a corn-based diet).