Cornflour is a term that can be used to refer to a number of different things, depending on geographical region and the intended use of the term. Typically, in the United States (US), cornflour refers to cornmeal that has been finely ground. Throughout much of the United Kingdom (UK), cornflour is typically used to refer to cornstarch, which is the starch taken from the corn grain itself. The term can also be used to refer to masa harina, a finely powdered flour made from corn that has been slaked and then ground.
In the US, cornflour is typically used by chefs, recipe books, and in home and professional kitchens to refer to cornmeal. Cornmeal is a powder of various degrees of coarseness that consists of corn, or maize, which has been ground using one of a number of different methods. When cornmeal is ground especially fine, it is often referred to as cornflour as it more closely resembles the fine powder of flour rather than the more coarse grains many people think of when considering cornmeal. This type of cornmeal can be used in a number of recipes and is often used on the bottoms of baked goods to make removal from ovens and baking surfaces easier.
Throughout the UK, the term cornflour is often intended to refer to cornstarch rather than the often coarse cornmeal. Cornstarch is usually produced by soaking whole kernels of corn and removing the germ of the corn from the endosperm and further breaking down each part until the starch is ultimately extracted from each. This starch is often a very fine powder that is usually used to make powdered sugar or added to sauces and soups to thicken them. Cornstarch is typically added to a small quantity of liquid and stirred together, then this is added to a soup or sauce and when heated will thicken the liquid.
In other areas, cornflour is often used to refer to masa harina or masa flour. This type of flour is made by first soaking corn kernels in a bath of water mixed with lime or ash, a process often referred to as slaking. The corn is then removed from the mixture and washed off before the hull of the corn is removed. This leaves the inner part of the corn, which is ground down into a very fine powder, similar to flour. Cornflour such as this is often used in making corn tortillas and tamales and may be made from yellow, white or blue corn.