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Soap   : Sodium or potassium salt of a long chain fatty acid is called soap .Soap is obtained by alkaline hydrolysis of oils /fats (tri glycerides )Soap do not give lather with hard water . The  most common form of soap is sodium stearate .

Detergents  :  Any substance which has the cleansing properties in water is called a detergent .This means any substance which can remove grease and dirt from any fabric or body is called a detergent .Common soap is a typical detergent .

   Now a days the detergent is used  only for synthetic detergents .In detergents the hydrophilic groups are sulphate (SO^4- )or sulphonate(SO^3-)  groups .Detergents can be classified as cationic,anionic and nonionic .Linear alkylbenzene sulphonate is the most common anionic detergent .Synthetic detergents have cleansing power as good or better than ordinary soap .The synthetic detergents are superior to soaps because they do not form insoluble salts with Ca^2+,Mg²⁺ and  Fe ³⁺ ions as soap do .Detergents can be used in either soft water or hard water .