A colloid, or colloidal dispersion, is a form of matter intermediate between a true solution and a mixture or suspension. Microscopic particles of one substance, said to be in the dispersed or solute phase, are distributed throughout another, said to be in the dispersing, continuous, or solvent phase.

Colloidal size - 0.001 micron to 1 micron in any dimension. Dispersions where the particle size is in this range are referred to as colloidal aerosols, colloidal emulsions, colloidal foams, or colloidal suspensions.

Colloids can be classified as follows:

  Dispersed Phase
Gas
Liquid
Solid
Dispersing Phase Gas - Liquid aerosol,
e.g.: fog, mist		 Solid aerosol,
e.g.: smoke, dust
Liquid Foam,
e.g.: whipped cream		 Emulsion,
e.g.: milk, mayonnaise, hand cream		 Sol,
e.g.: paint, ink
Solid Solid foam,
e.g.: styrofoam		 Gel,
e.g.: gelatin, jelly, cheese		 Solid sol,
e.g.: ruby glass