A class of high-molecular-weight molecules, usually with colloidal properties, which in an appropriate solvent or swelling agent are able to produce gels (highly viscous suspensions or solutions) at low dry-substance content. The molecules are either hydrophilic or hydrophobic; that is, they do or do not have an affinity for water. The term gum is applied to a wide variety of substances of gummy characteristics, and therefore cannot be precisely defined.