Lipid: Another word for "fat." (Please see the various meanings of fat.) A lipid is chemically defined as a substance that is insoluble in water and soluble in alcohol, ether, and chloroform.

Lipids are an important component of living cells. Together with carbohydrates and proteins, lipids are the main constituents of plant and animal cells.

Cholesterol and triglycerides are lipids. Lipids are easily stored in the body. They serve as a source of fuel and are an important constituent of the structure of cells.

Lipids include fatty acids, neutral fats, waxes and steroids (like cortisone). Compound lipids (lipids complexed with another type of chemical compound) comprise the lipoproteins, glycolipids and phospholipids.