Colloidal dispersions are a class of soft materials. The term typically refers to a material consisting of solid particles spread throughout a fluid. According to Jones (p. 49), colloidal particles must have dimensions on the order of 10<math>\mu</math>m or smaller.
Witten (p. 113) distinguishes between colloids (solid particles in liquid), emulsions (liquid drops in another liquid), and foams (gas bubbles in a liquid), while Jones (p. 1) includes emulsions as a subgroup of colloids.
R. Jones, "Soft Condensed Matter," Oxford University Press Inc., New York (2002).
T. Witten, "Structured Fluids: Polymers, Colloids, Surfactants," Oxford University Press Inc., New York (2004).