Updated January 16th, 2022
Icing Sugar is also known as Powdered sugar, Confectioners sugar or 10x Sugar.
It is a granulated sugar that has been ground to a powder and then sifted. Typically a small amount of cornstarch is blended in to stop clumping.
Icing Sugar may give baking a better quality as the finer sized grains dissolve faster than granulated sugar and won't leave a gritty texture in your recipe.
You can make your own Icing Sugar simply by grinding regular table sugar into a fine powder with a spice grinder. If you plan on storing it for a later use, add a pinch of cornstarch.
Convenient and economical.
Usually found in the Baking Needs & Mixes Aisle.