Cornmeal is a meal (coarse flour) ground from dried maize (corn). It is a common staple food, and is ground to fine, medium, and coarse consistencies, but not as fine as wheat flour. In the United States, very finely ground cornmeal is also referred to as corn flour. When fine cornmeal is made from maize that has been soaked in an alkaline solution, e.g., limewater (a process known as nixtamalization), it is called masa, which is used for making tamales and tortillas. Boiled cornmeal is called polenta. (source)