Two or more substances combined so as to leave their chemical properties intact. Mixtures should not be confused with compounds.

Compounds have properties that differ from those of their components, their composition is fixed, and they cannot be easily broken down into their components.

Mixtures have the same properties as their components, their composition is variable, and they can be easily broken down into their components. Mixtures can be homogeneous, i.e., with identical characteristics in any given point (solutions), or heterogeneous, i.e., with different characteristics in different points (fumes, fog, emulsions, and suspensions).