Ditto to the others 0% is skim milk.
However ... perhaps you are asking the difference between skim milk processed the original way and the newer pur-filtered or fine-filtered milks?
Because of the process they go thru, they do tend to seem richer, and are often advertised as seeming to be more like a milk with butterfat (as in 1% or 2%)
Would this be the question you were posing?