As shown in the picture, when 3 fatty acids and 1 glycerol combine, they form a triglyceride. As a by-product, 3 water molecules must be lost in the reactants side, and would appear in the product side to obey the law of conservation of mass. Fatty acids are long chains of hydrocarbon with carboxylic acid tails. On the other hand, glycerol is the backbone of a triglyceride which has 3 hydroxyl groups attached.