Potassium Hydroxide is a type of lye specifically used to make liquid soap. It is also known as potash, lye or even KOH. This is the chemical that induces saponification of the fats and oils to create liquid soap.
Potash can actually be used to make liquid soaps, bar soaps and jelly soaps by adding NaOH of course for solid soaps. You can use all types of potassium salts to saponify lipids