Frosting: A sweet glaze often made with sugar, butter, water and egg whites or milk, often flavored and cooked (although it can be uncooked). It's used to cover or decorate baked goods, such as cakes or cookies and can range from thick to thin.
Icing: see Frosting. Yep that's right, the words are interchangeable. Often frosting is actually a type of icing, but it depends on where you're from.
Frosting and icing seem to be words that vary by region. So how about you, what do you call it?