caster sugar       
noun [ U ] UK (also castor sugar) uk/ˈkɑː.stə ˌʃʊɡ.ər/ us/ˈkæs.tɚ ˌʃʊɡ.ɚ/ (US superfine sugar)
 精白砂糖
white sugar with very small grains, often used in cooking
  Sprinkle a teaspoon of caster sugar over the top.
 Cream together the butter and caster sugar.
 Compare: brown sugarconfectioner's sugardemerara sugargranulatedicing sugarpowdered sugarsuperfine sugar
 - More examples
 - You need 3 eggs and 6 ounces of caster sugar.
 - Place the eggs and caster sugar in a mixing bowl and whisk with an electric mixer until thick and mousse-like.
 - Dissolve the caster sugar in water and boil to make a syrup.
 - Weigh out 100g plain flour and 200g caster sugar.