When the fats are reacted with alkali, they form 'soaps'. The type of reaction taking place in the formation of soaps is called _________.

When the fats are reacted with alkali, they form soaps. The type of reaction taking place in the formation of soaps is called saponification.

Soaps are sodium or potassium salts of long chain fatty acids. When triglycerides in fat/oil react with aqueous $NaOH$ or $KOH$, they are converted into soap and glycerol. This is called alkaline hydrolysis of esters. Since this reaction leads to the formation of soap, it is called the Saponification process.