What is a soft soap?

Soaps are sodium or potassium salts of long-chain fatty acids,such as palmitic acid $(C_{15}H_{31}COOH)$,stearic acid $(C_{17}H_{35}COOH)$,and oleic acid $(C_{17}H_{33}COOH)$.
Potassium salts of these fatty acids are known as soft soaps. They are more soluble in water and are used in shaving creams and shampoos.
The reaction for the preparation of potassium stearate (a soft soap) is:
$(C_{17}H_{35}COO)_3C_3H_5 + 3KOH \rightarrow 3C_{17}H_{35}COOK + C_3H_5(OH)_3$
(Glyceryl ester of stearic acid + Potassium hydroxide $\rightarrow$ Potassium stearate + Glycerol)