Both icing and powdered sugars are used on baking. Essentially there are no differences between them. These two words are interchangeable with one another and have the same meaning. Other names the two have are icing cake, 10x sugar, and confectioners sugar.
They both can vary in fineness, which depends on how the person chooses to make it. Icing and Powdered sugars can be made at home by the everyday cook, as well as by professional bakers and chefs. A chef also sees no difference between them and will use the words interchangeably. These sugars date back to 1769 when Elizabeth Raffald was the first to use it.