[ih-MUHL-shuhn] An emulsion is a mixture of two liquids which cannot normally — oil and water is the classic example. Emulsifying is done by slowly, adding one ingredient to another while mixing rapidly. This action helps to disperse and suspends the tiny droplets of one liquid throughout the other.

Culinarily, emulsified mixtures typically have a thick and satiny texture. Mayonnaise and Hollandaise are two of the best known emulsions.  

References