The Solubility Product, Ks, is the equilibrium constant for the equilibrium that exists between a slightly soluble salt and its ions in a saturated solution. For example,
AgCl(s) = Ag+(aq) + Cl-(aq)
Ks = [Ag+(aq)][Cl-(aq)] Ks = 1.74 x 10-10 mol2 dm-6
Solubility product and 'solubility' are different and must not be confused. Unlike the solubility of a substance, the solubility product is independent of what else is dissolved in solution. The solubility of a substance can be calculated from its solubility product.
See also Equilbrium Constant.