Being an American, I was used to just picking up a bag of granulated sugar at my local supermarket when I wanted to do baking. The only issue I had with sugar was to make sure it was pure cane sugar - no corn sugar, no maltose, etc added (to cheapen and stretch the product).
But, when I moved to the UK and bought what was labeled as pure cane granulated sugar something was different, wrong, weird. It looked wrong, it didn't dissolve right in coffee or in batter mixes.
The problem was classic - same names for different things. In the UK, what I thought of as granulated sugar was called Castor sugar. Now the experts on the web claim that Castor sugar in the UK is the equivalent of Superfine sugar in the US. Perhaps. But UK granulated sugar is absolutely not the same as US granulated sugar. End of.
So if I call for castor sugar in a recipe - and you are in the US, just use granulated sugar.
With liquids we get a whole new set of issues. They still have cups and pints here - but they are also very different. For example: US pint = 16 oz, UK pint = 20 oz
I try to be careful about these issues when I post recipes.