A beta-galactoside is a type of galactoside in which the glycosidic bond lies above the plane of the galactose residue. The most commonly recognized and used beta-galactoside in biochemistry is Lactose. However, other chemicals, such as ONPG, are known, but these are typically synthesized for biochemical assays. An enzyme that breaks the beta-galactoside bond is called a beta-galactosidase.