Powdered sugar (confectioner’s sugar) is sucrose that has been crushed under immense pressure to create a fine powder. It is rated using an X system (XXX, 6X, 10X). The amount of Xs indicates the fineness of the sugar. The amount of Xs indicates the amount of times the sugar was pulverized. Powdered sugar, generally, contains 3% cornstarch, which acts as an anti-caking agent.
Powdered sugar has a number of culinary applications. Technically, it can be used in any recipe that calls for sugar as a sweetener. Although, the product would be drastically different in situations in which a specific type of sugar is needed for the structure of the finished product. In America, it is mostly used to create icings and frostings.