a saccharide polymer containing a small number (typically two to ten) of simple sugars (monosaccharides)

An oligosaccharide is a polymer of a few different simple sugars. Oligosacchardides are carbohydrates. When they are hydrolized, oligosaccharides give 3 to 10 monosaccharides.

Shown is a branched oligosaccharide made of three sugars

Oligosacharides are formed when 3 to 10 monosaccharide units combine with each other by the loss of water molecules, resulting in the formation of a glycosidic linkage. Conversely hydrolysis of an oligosaccharide in water in the presence of an acid or enzyme yields 3 to 10 monosaccharide units. Oligosaccharides which consist of two monosaccharides units are called as disaccharide. Oligosaccharides containing 3 monosaccharides are called trisaccharides.