An emulsion is a mixture of two or more liquids that are normally immiscible (nonmixable or unblendable). Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms ''colloid'' and ''emulsion'' are sometimes used interchangeably, ''emulsion'' should be used when both the dispersed and the continuous phase are liquids. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Examples of emulsions include vinaigrettes, milk, mayonnaise, and some cutting fluids for metal working. The photo-sensitive side of photographic film is an example of a colloid.