Short answers, pulled from the story.
Lipids are a broad group of organic compounds that include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, and phospholipids. Their functions include storing energy, signaling, and acting as structural components of cell membranes. They are defined as hydrophobic or amphiphilic small molecules.
The Lipid MAPS consortium classifies lipids into eight categories: fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids, and polyketides, which derive from ketoacyl subunits, plus sterol lipids and prenol lipids, which derive from isoprene subunits.
The word stems from the Greek lipos, meaning fat. The French pharmacologist Gabriel Bertrand introduced the word lipide in 1923, and it was approved unanimously by the international commission of the Societe de Chimie Biologique on the 3rd of July 1923. It was later anglicized as lipid.
The complete oxidation of fatty acids releases about 38 kJ/g, or 9 kcal/g, compared with only 17 kJ/g, or 4 kcal/g, for the oxidative breakdown of carbohydrates and proteins. Triglycerides stored in adipose tissue are a major form of energy storage in animals and plants.
Linoleic acid, an omega-6 fatty acid, and alpha-linolenic acid, an omega-3 fatty acid, are essential fatty acids that mammals cannot synthesize from simple precursors and must obtain from the diet. Both are 18-carbon polyunsaturated fatty acids differing in the number and position of their double bonds.
Glycerophospholipids are the main structural component of biological membranes and form a lipid bilayer through the hydrophobic effect. In an aqueous environment the polar heads align toward the water while the hydrophobic tails cluster together, producing micelles, liposomes, or bilayers depending on concentration.