What is the ionic product of water ? a level chem

Which one of the following statements best describes what is meant by the ion product of water:
1.The product of the concentrations of hydrogen ions and hydroxyl ions that are derived only from water molecules in aqueous solution of electrolytes
2.The product of the concentrations of hydrogen ions and hydroxyl ions in water or in aqueous solutions of electrolytes
3.The number of ionized molecules of H2O in 1 mole of pure water
4.The total number of negatively and positively charged ions in 1 L of an aqueous solution of an electrolyte

I would say 2 ?