Unsaturated fat, a fatty acid in which the hydrocarbon molecules have two carbons that share double or triple bond(s) and are therefore not completely saturated with hydrogen atoms. The generic formula for an unsaturated fatty acid with only one double bond is R-COO–, with R representing the chemical grouping CH3(CH2)mCH=CHCH2(CH2)n. If m=n=7, this would represent the 18-carbon unsaturated fatty acid oleate (oleic acid).