The maximum number of undissociated ions, of an electrolyte in asaturated solution, capable at a given temperature of remaining inequilibrium with the undissolved phase of the solution.
Solubility product is defined as the product of ionic concentration when dissolved ions and undissolved ions are in equilibrium. In other words, When a saturated solution of sparingly or slightly soluble salt is in contact with undissolved salt, an equilibrium is established between the dissolved ions and the ions in the solid phase of the undissolved salt. Ionic product at this stage is called solubility product.
Determination of solubility product:
Consider a slightly soluble salt such as silver chloride (AgCl).