Sugar

Simple, water soluble, carbohydrates, for exambple monosaccharides, disaccharides and oligosaccharides, may loosly be reffered to as 'sugars'.  They contain either an aldehyde of a ketose group and also contain -OH groups. By changing the orientation of the -OH groups around the carbon atoms can change the type of sugar. Sugars have the emperical formula CH2O and usually containg between 3 and 8 carbon atoms.

[Molecular Biology of the cell, Alberts et. al]