In chemistry, a glycoside is any molecule in which a sugar group is bonded through its anomeric carbon to another group via an O-glycosidic bond or an S-glycosidic bond; the latter are also called thioglycosides. Glycosides play many important roles in living organisms, and numerous plant-produced glycosides are used as medications.
The above definition is the one used by IUPAC. Many authors require in addition that the sugar be bonded to a non-sugar for the molecule to qualify as a glycoside, thus excluding the polysaccharides. The sugar group is then known as the glycone and the non-sugar group as the aglycone or genin part of the glycoside. The glycone can consist of a single sugar group (monosaccharide) or several sugar groups (oligosaccharide).