The simplest lipids constructed from fatty acids are the triacylglycerols, also referred to as triglycerides, fats, or neutral fats. Triacylglycerols are composed of three fat acids each in ester linkage with a single glycerol. Because the polar hydroxyls of glycerol and the polar carboxylates of the fatty acids are bound in ester linkages, triacylglycerols are nonpolar, hydrophobic molecules, essentially insoluble in water.

In most eukaryotic cells, triacylglycerols form oily droplets in the aqueous cytosol, serve as depots of metabolic fuel. Specialized cells in vertebrate animals, called adipocytes, or fat cells, store large amounts of triacylglycerols as fat droplets, which nearly fill the cell. Triacylglycerols are also stored in the seeds of many types of plants, providing energy and also and biosynthetic precursors when seed germination occurs.