Lipid
A biomolecule that is largely non-polar and therefore insoluble in water but soluble in organic solvents.
Unit
Dimensionless
In depth
Lipids are defined by solubility rather than by a common structure, so the class includes fats, phospholipids, steroids and waxes. They store more than twice as much energy per gram as carbohydrates, insulate, cushion organs and form every cell membrane.
Examples in the real world
Butter and olive oil as triglycerides; cholesterol as a steroid; beeswax as an ester of long-chain acids and alcohols.