a sugar comprising one glucose molecule linked to a galactose molecule; occurs only in milk
"cow's milk contains about 4.7% lactose"
The disaccharide sugar of milk and dairy products, C₁₂H₂₂O₁₁, a product of glucose and galactose used as a food and in medicinal compounds.
"After learning that lactose is the primary sugar found in milk, she decided to try a lactose-free yogurt instead."