Does the 4 sticks of butter refer to 1/2 cup sticks or 1 cup sticks?

It looks like it has since been updated, but just to add, I've never seen a recipe where a stick of butter was a 1 cup stick. It's always been 1 stick = 1/2 cup = 8 Tablespoons, and I've probably made about 1,000 dessert recipes. So that would be the most likely thing that the author meant :)

Each stick would be 8 tablespoons or 1/2 cup or 4oz. To make the frosting you would need 1 pound of butter