Caster sugar refers to a type of sugar that has very fine granules. It is often used in baking to dissolve quickly in recipes such as cakes and meringues. Full definition
Two hours before baking, in a bowl combine sliced strawberries, liqueur and a tablespoon of caster sugar in a bowl. (butterandbrioche.com)
I keep a jar of golden caster sugar with spent vanilla pods immersed in it. (tinandthyme.uk)
Melted 1/4 a cup of golden caster sugar in a pan over medium heat, then allowed to simmer for a couple of minutes until it turned a bronzy colour. (tinandthyme.uk)