do they mean you will visibly see it or when you weigh yourself it shows or both?
obviously. but what I mean is symptoms for medicines, shots, etc. does it mean you look fatter or you are heavier?
Well, if you weighed 120 pounds, and now you weigh 123 pounds, you gained weight. Whether you see it or not.
weight is different than mass, but weight gain is weight gain whether you see it or not