Knowing the categories/types of icings and their makeups can help you improve your decorated cake offerings. Here is a quick primer that Kirk O'Donnell shared at the 2011 All Things Baking show in Schaumburg, IL this month.

Types of Icings

Non-aerated (flat icings)
Pouring icings
Confectionery coatings
Fudges/fondants

Partially aerated
Buttercreme icings
Buttercreme fillings

Aerated (foam type)
Marshmallow
Whipped cream
Whipped toppings

Below are examples of two non-aerated icings and their makeup and common uses:

Pouring Icings
Used for specialty cakes, donuts, Danish, sweet dough
Powdered sugar: 80-85%
Water: 5-20%
Ingredients: Sugars, water, stabilizers, fats, salt, calcium carbonate, titanium dioxide, calcium sulfate, sodium hexametaphosphosphate

Confectionary Coatings
Used for cookies, snack cakes, petit fours, specialty cakes, donuts
Powdered sugar: 55-60%
Hard fats: 30-35%
Ingredients: Powdered sugar, hard fats, milk powder, lecithin, natural cocoa, cocoa butter, salt and vanillin