Icing Sugar or Confectioner's Sugar is white or creamy white and very finely textured. It is made by grinding sugar down to a powder.
Icing sugar tends to clump up, so will need sieving whatever the brand. In fact, clumping up is good as it means there are no additives to make it free flowing. But if it does contain an anti-caking agent, this should be starch or calcium phosphate.
Icing sugar is fine, creamy and smooth, and very sweet.
Icing sugar's superfine texture makes it spot-on for smooth icings, the creamiest frostings and butter creams, or for dusting Turkish delight. Icing sugar dissolves straight away so is good mixed into cream to sweeten it up, or in truffles. It can also be used for meringues.