The active ingredient in some soaps. It used to be the active ingredient in nearly all soaps, but has been superceded somewhat by new chemicals with weird names. Homemade soap and glycerine soap are very likely to use sodium stearate.
Sodium stearate is produced by a saponification reaction of animal fat (lard, chemical name glyceryl tristearate) and sodium hydroxide (lye).
CH2(CH2)16COOCH(CH2)16COOCH2(CH2)16COO + 3NaOH ----->
CH2CHCH2(OH)3 + 3(CH3{CH2}16COONa)
The glycerine produced is usually removed from the soap product and sold, usually to be combined with a mixture of nitric and sulfuric acid to create nitroglycerine, a quite potent and sensitive explosive. However, glycerine soap keeps the glycerine in the soap product. It supposedly helps your skin.