The term refers to a state of subdivision, implying that the molecules or polymolecular particles dispersed in a medium have at least in one direction a dimension roughly between \(1\ \text{nm}\) and \(1\ \unicode[Times]{x3BC}\text{m}\), or that in a system discontinuities are found at distances of that order.
PAC, 1972, 31, 577. (Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry) on page 605 [Terms] [Paper]