2% milk is called 2% milk because the milkfat constitutes 2% of the total weight of the milk.
In other words, the "2%" refers to the percentage of milkfat by weight in the final product. It's important to note that this doesn't mean 2% of your glass of milk is fat. Rather, if you were to weigh the components of the milk, the fat content would account for 2% of that total weight. For example, if you have 100 grams of 2% milk, 2 grams of that would be fat.
It's a common misconception that "2%" refers to the percentage of fat removed from whole milk, but it indicates the final fat content relative to the milk's total weight.
