Field corn is the common name for the corn traditionally grown by farmers to feed their livestock. It can be fed fresh or stored in several ways to feed during the winter months. (It is often fed all year long).
It can be stored as EAR corn - dried corn on the cob. It is often ground before feeding as cattle have a hard time eating whole ears of corn.
It can be stored as SHELL corn. Dried corn off the cob. This can be fed as is or ground into a meal. It is often an ingredient in many different animal grains or feds.
It can be stored as SILAGE. This is often the whole corn plant (ears, corn, stem, husk) all chopped into inch or so sized pieces. These are then packed into the tall upright silos, into cement bunkers or into storage bags. It is then allowed to ferment until needed to be fed.
Other uses of field corn are for fuel sources. I actually heat my home with dried shell corn. Ethanol is often made from corn.
This is just a sample of the uses of field corn. (You can eat it yourself, but it is not as tasty as sweet corn.)