Solubility is the property of a solid, liquid, or a gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. It is usually expressed in grams per 100 g of solvent at a specified temperature.

According to the IUPAC definition, solubility is the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in various units of concentration such as molarity, molality, mole fraction, mole ratio, mass (solute) per volume (solvent), and other units.

The system of analysis used for identifying the metallic ions present in a mixture of inorganic compounds depends upon the very low solubilities of certain salts of the metals.