Lipids are organic compounds, the common and defining feature of which is their insolubility in water, where it forms micelles, and can be extract from cells and tissues by a nonpolar solvent.

Fats and oils are the principal stored forms of energy in many organisms, phospholipids and sterols make up about half the mass of biological membranes. Other lipids, although present in relatively small quantities, play crucial roles as enzyme cofactors, electron carriers, light-absorbing pigments, hydrophobic anchors, emulsifying agents, hormone and intracellular messengers.

The main lipids are triacylglycerols, waxes, glycerophospholipids, sphingolipids and sterols.