noun, plural: lipids
A fatty or waxy organic compound that is readily soluble in nonpolar solvent (e.g. ether) but not in polar solvent (e.g water). Its major biological functions involve energy storage, structural component of cell membrane, and cell signaling.
Fatty acids (including fats) are a subgroup of lipids, hence, it will be inaccurate to consider the terms synonymous.
Compare: fatty acid.