An oligosaccharide, a sugar, is a saccharide polymer containing a small number monosaccharides (simple sugars). An oligosaccharide commonly refers to a carbohydrate polymer whose molecules are composed of a relatively small number of monosaccharide units. The parameters for an oligosaccharide vary, however they are typically counted as any sugar with between 3 and 9 monosaccharide units. Oligosaccharides are formed when two or more monosaccharides join together by O-glycosidic bonds. Examples include sucrose, lactose and maltose. Specific enzymes are used to catalyze the glycosidic bonds in oligosaccharides and each sugar must be specific to each enzyme used for each new glycosidic bond.