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

and

,
or that in a system discontinuities are found at distances of that order.
Source:
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