"Milk derivatives" refers to substances or ingredients that have been derived or made from milk. These derivatives can include products like butter, cheese, cream, or powdered milk. Full definition
To keep to your lactose free diet you may need to watch out for other milk derivatives too, many milk products are added to processed foods in various guises so keep and eye on the labels and look our for: milk, lactose, whey, curds, milk by - products, non-fat dry milk powder. (goodnessdirect.co.uk)
Does not contain citrus, MSG, wheat, gluten, corn, starch, sugar, soy, yeast, zein, sulfate, phosphates (other than coenzymes), preservatives, casein or other milk derivatives. (acuatlanta.net)
In addition, some people get their protein from supplements such as whey protein powder which is a milk derivative. (fitnessandpower.com)