As far as I know, lipids are defined as biomolecules which are hydrophobic.
Triglycerides are composed of fatty acids and glycerol and are considered lipids but, are fatty acids alone or glycerol alone considered as lipids ?
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From IUPAC Goldbook:
A loosely defined term for substances of biological origin that are soluble in nonpolar solvents. They consist of saponifiable lipids, such as glycerides (fats and oils) and phospholipids, as well as nonsaponifiable lipids, principally steroids.
That means that lipid does not mean any hydrophobic molecule. Lipids can be amphipathic as you already know about fatty acids.
Glycerol is not a lipid; neither is it hydrophobic. Glycerol, if to be classified into one of biomolecular classes, it would be that of monosaccharides (in the form of sugar alcohol like sorbitol and xylitol).
Lipids may be broadly defined as hydrophobic or amphiphilic small molecules; the amphiphilic nature of some lipids allows them to form structures such as vesicles, multilamellar/unilamellar liposomes, or membranes in an aqueous environment.