What is an emulsion?

An emulsion may be defined as a heterogeneous system consisting of two immiscible liquid phases in which one liquid is intimately distributed in the other as minute droplets whose diameters exceed 0.1 micrometer. In most cases one of the liquids is water. A third component, known as a surfactant (emulsifying agent or stabilizer), must be present in amounts adequate to prevent coalescence of the dispersed phase.