Powdered Sugar is useful as icing sugar on top of cakes and donuts. It is pure sugar milled to create soft powdery form. Other than cakes and donus, Powdered Sugar is also good for drinks and desserts.
Good Powdered Sugar is the one that does not clot. Clotting of Powdered Sugar makes it difficult to handle for perfect distribution of icing, and not ease of solving in your favorite drink. Good Powdered Sugar is also the one that is not mixed with corn starch to dilute the sugar content, but rather pure sugar.