Cornmeal is ground up corn. It is not to be confused with cornstarch or corn masa. Both cornstarch and finely-ground cornmeal are sometimes called cornflour; thus, this term can be imprecise or vague.
Cornmeal can be applied to wet items, drying them off so that batter will stick. This is commonly done for deep-fat frying. When a recipe uses cornmeal in this way, you can often substitute flour or cornstarch. Some variations of the batter for deep-fat frying also contains cornmeal.