Fatty acids are aliphatic monocarboxylic acids derived from or contained in esterified form in an animal or vegetable fat, oil or wax. Natural fatty acids commonly have a chain of 4 to 28 carbons (usually unbranched and even-numbered), which may be saturated or unsaturated. By extension, the term is sometimes used to embrace all acyclic aliphatic carboxylic acids. (Source: IUPAC Gold Book)
Fatty acids instead of their free form are usually found in the form of esters in living creatures. Triglycerides, phospholipids and cholesterol esters are three main classes of esters that contain fatty acids in their esterified forms. Such biomolecules have their own important biological roles like structural components for cells and fuel sources for animals.
Beside their important roles in living creatures, fatty acids are also important industrially. In many cases, industries use hydrolysis of triglycerides or phospholipids to produce required fatty acids but in the case of some fatty acids other alternative methods like hydrocarboxylation of alkenes may also exist. One major use of fatty acids is production of soaps for both cleansing and lubricating products. Fatty acids are also consumed as precursors for fatty alcohols, fatty amines and some esters which are consumed as or are used to produce chemicals like surfactants, detergents, lubricants, emulsifiers, texturizing agents, wetting agents, anti-foam agents and stabilizing agents or even constituents of food products.