In Australia icing sugar in comes in two forms:
Pure Icing sugar: extremely refined white sugar that must be broken down through a sieve before measuring and using. Use for dusting cakes and the like and in sweet pastry recipes.
Icing Sugar Mixture: pure icing sugar mixed with cornflour to keep it smooth. Usually used for ‘easy to manage’ icings.
Pure icing sugar is also called confectioner’s sugar in some recipes.