Frosting is the sweet, spreadable covering on a cake, made from very fine sugar mixed with butter, and often a little milk or flavour. Americans say frosting for this; British people more often say icing, and may keep frosting for a thick, buttery kind. In the kitchen, to frost a cake is to put that covering on. The word comes from frost, because a finished cake can look a little as if overnight cold has left a white coat on it. Though actually, frosting is not the same thing as frost on a window, and it is not the thin, shiny sugar shell on a doughnut — that is more of a glaze. Baker-shop English, informal, very common in American recipes.