1) A sample of matter composed of two or more substances, each of which retains its identity and properties.
2) an association of substances, which cannot be represented by a chemical formula. In a heterogeneous mixture the substances are not uniformly dispersed, as is the case in Italian salad dressing. In the purest sense, the term "homogeneous" refers to a chemical composition of only one compound or element, but the term "homogeneous mixture" is loosely used to describe two or more substances that are uniformly dispersed as in a solution of water and sodium chloride (table salt).