I will just paste the argument from wikipedia, which redirects corn to maize. Basically, as you will read, the word corn actually means lots of different kinds of plants, and maize is much more specific. "Maize" is precise, "corn" is ambiguous "Maize" is the vernacular word that means only the plant that this article is about, in all regional varieties of English. "Corn" has a confusing variety of meanings that vary by locality. In particular, one common meaning of "corn" is the staple cereal crop of a given locality. 3a. collective singular. The seed of the cereal or farinaceous plants as a produce of agriculture; grain. As a general term the word includes all the cereals, wheat, rye, barley, oats, maize, rice, etc., and, with qualification (as black corn, pulse corn), is extended to leguminous plants, as pease, beans, etc., cultivated for food. Locally, the word, when not otherwise qualified, is often understood to denote that kind of cereal which is the leading crop of the district; hence in the greater part of England ‘corn’ is = wheat, in North Britain and Ireland = oats; in the U.S. the word, as short for Indian corn, is restricted to maize (see 5). 5. orig. U.S. Maize or Indian corn, Zea Mays; applied both to the separated seeds, and to the growing or reaped crop. corn on the cob: green maize suitable for boiling or roasting; maize cooked and eaten on the cob. Wheat, rye, barley, oats, etc. are in U.S. called collectively grain. Corn- in combinations, in American usage, must therefore be understood to mean maize, whereas in English usage it may mean any cereal; e.g. a cornfield in England is a field of any cereal that is grown in the country, in U.S. one of maize.—Oxford English Dictionary's definition of "corn"
