1) The metabolic process of breaking down lipids to release free fatty acids, the major oxidative fuel for the body. Lipolysis may involve dietary lipids in the digestive tract, circulating lipids in the blood, and stored lipids in the adipose tissue or the liver. A number of enzymes are involved in such lipid hydrolysis, such as lipase and lipoprotein lipase from various tissues.

2) The chemical reactions and pathways resulting in the breakdown of lipids, compounds soluble in an organic solvent but not, or sparingly, in an aqueous solvent.