Powdered sugar, also known as confectioners' sugar or icing sugar, is very fine sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

. When intended for home use, it typically contains a small amount of anti-caking agent.

In industrial food production, it is used where a quick dissolving sugar is required. Domestically, it is principally used to make icing

Icing (food)

Icing, also called frosting in the United States, is a sweet often creamy glaze made of sugar with a liquid such as water or milk, that is often enriched with ingredients such as butter, egg whites, cream cheese, or flavorings and is used to cover or decorate baked goods, such as cakes or cookies...

 or frosting

Icing (food)

Icing, also called frosting in the United States, is a sweet often creamy glaze made of sugar with a liquid such as water or milk, that is often enriched with ingredients such as butter, egg whites, cream cheese, or flavorings and is used to cover or decorate baked goods, such as cakes or cookies...

 and other cake decorations

Cake decorating

Cake decorating is one of the sugar arts that uses icing or frosting and other edible decorative elements to make otherwise plain cakes more visually interesting...

. It is often lightly dusted on baked goods to add a light sweetness and subtle decoration.

Powdered sugar is available in different degrees of fineness, most commonly XXX, XXXX, and 10X, with more Xs indicating finer grains. Powdered sugar is generally mixed with cornstarch

Cornstarch

Corn starch, cornstarch, cornflour or maize starch is the starch of the corn grain obtained from the endosperm of the corn kernel.-History:...

, wheat flour, or calcium phosphate

Calcium phosphate

Calcium phosphate is the name given to a family of minerals containing calcium ions together with orthophosphates , metaphosphates or pyrophosphates and occasionally hydrogen or hydroxide ions ....

 to improve its flowing ability, and thus it is not generally used to sweeten beverages. However, industrial grades without these additives are available.

One can make powdered sugar at home by putting normal granulated sugar in a coffee grinder or grinding it by hand in a mortar and pestle

Mortar and pestle

A mortar and pestle is a tool used to crush, grind, and mix solid substances . The pestle is a heavy bat-shaped object, the end of which is used for crushing and grinding. The mortar is a bowl, typically made of hard wood, ceramic or stone...

.

Castor sugar (also referred to as superfine or baker's sugar) has a larger particle size, up to approximately half that of granulated sugar.

Snow powder (or snow sugar) is a non-melting form of icing sugar, useful for retaining its structure when dusted onto cakes or pastries that require refrigeration. It is mostly used for decorative purposes.