Corn starch, or maizena, is the starch coming from maize. Just like corn flour, it is considered a quite high-calorie flour.
Corn starch is a gluten-free flour with great thickening powers, so it is an important resource for coeliac-friendly recipes. It is also used as an anticaking agent, mainly in icing sugar.
It can be used ad a thickening agent in ice creams and other preparations, instead of eggs. It also is a valuable substitute of barley in beer production.
Fun fact: besides its cooking uses, it is also used to make biodegradable shopping bags, in paper manufacturing, as anti-stick agent on medical products, and to make skin emollient products.