Noun
One of the constituents of animal fats and also of some vegetable fats, as the butter of cacao. It is especially characterized by its solidity, so that when present in considerable quantity it materially increases the hardness, or raises the melting point, of the fat, as in mutton tallow. Chemically, it is a compound of glyceryl with three molecules of stearic acid, and hence is technically called tristearin, or glyceryl tristearate.
Source: Webster's dictionary