A solution is a homogeneous mixture of two or more substances, which can be ions, molecules, or both.  A colloidal solution appears to be a homogeneous solution but in fact consists of relatively large particles of one or more substances in one phase dispersed throughout a second phase.  A foam is defined chemically as a colloidal dispersion of a gas in a liquid or solid.

Ice cream is an edible example of a foam in which air bubbles are dispersed throughout a mixture of liquid water, solid fat globules, and ice crystals.  The reason ice cream is not a solid block of ice is the colligative properties of the aqueous solutions embedded in it:  the liquid phase consists of tiny droplets of water that contain dissolved sugars, salts, and suspended milk proteins.  The presence of these dissolved components lowers the freezing point so that the liquid phase stays liquid, even at a typical freezer temperature of -18 °C (0 °F).

Ice cream is an edible example of a foam in which air bubbles are dispersed throughout a mixture of liquid water, solid fat globules, and ice crystals. (V. Holtgrewe)

Dissolved salts are especially important because they lower the freezing point of the mixture more than a nonionic molecule.  In dilute solution, a salt that dissociates into two ions lowers the freezing point twice as much as a molecule that doesn't dissociate at all.  However, this trend is not observed for more concentrated solutions because the ions begin interacting with one another, and the freezing point is not as depressed as one might expect.

The solid fat globules provide most of the smoothness and "body" of ice cream.  The function of the ice crystals, which should be small (50 µm in diameter) to avoid a coarse and icy texture, is to stabilize the foam.  The dispersed air bubbles make ice cream lighter and softer and therefore easier to scoop and eat. Commercial ice cream adds even more air than is introduced in homemade ice cream, in part because this results in less ice cream per quart and ice cream is sold on a volume, not weight, basis.

Reger/Goode/Mercer:  Chemistry Principles and Practice,  2/e,  pp. 504–505