Icing sugar, also called confectioner’s sugar or powdered sugar, is a finely ground sugar made by milling normal granulated sugar into a powdered state. It usually contains a small amount of anti-caking agent to avoid clumping and improve flow.
Although most often produced in a factory, it can also be made by putting normal sugar in a coffee grinder, or crushing it by hand in a mortar and pestle.
In industrial food production, it is used where a quick dissolving sugar is required. Domestically, it is principally used to make icing or frosting and other cake decorations. It is often lightly dusted onto baked goods to add a light sweetness and delicate decoration.