Also called powdered sugar and confectioners' sugar, icing sugar is granulated white sugar that’s been pulverized to a powder and mixed with a small but mighty amount of cornstarch. It is utilized in industrial food production when a quick-dissolving sugar is required. Home cooks use it principally to make icing or frosting and other cake decorations, not to mention that it is often dusted onto baked goods to add a subtle sweetness and delicate decoration.