(1) Lipid is a fatty substance found in the blood. Lipid metabolism is the conversion of the fat molecule from fat to energy (and other by-products).
(2) lipid /lip·id/ (lip´id) any of a heterogeneous group of fats and fatlike substances, including fatty acids, neutral fats, waxes, and steroids, which are water-insoluble and soluble in nonpolar solvents. Lipids, which are easily stored in the body, serve as a source of fuel, are an important constituent of cell structure, and serve other biological functions. Compound lipids comprise the glycolipids, lipoproteins, and phospholipids.
See also: Lipid