Definition: Corn Gluten Meal: the dried residue from corn after the removal of the larger part of the starch and germ, and the separation of the bran by the process employed in the wet milling manufacture of corn starch or syrup, or by enzymatic treatment of the endosperm.
Corn is a popular filler in "grocery store" pet foods, as it is a cheap filler, as well as a cheap source of protein. It is also one of those products that often cause allergies in cats. If I had to choose a product containing corn, I'd probably go for corn meal, which also includes the germ.
However, since cats are obligate carnivores and don't really need a large amount of carbohydrates, I eschew corn in any form in the food my cats eat.