Any of a class of organic compounds made from the chemical reaction between an alcohol and an organic acid. The transesterification of vegetable oils, animal fats or waste cooking oils is the process behind conventional biodiesel.

In the transesterification process a glyceride reacts with an alcohol (typically methanol or ethanol) in the presence of a catalyst forming fatty acid alkyl esters and an alcohol (glycerol) (source: ETIP Bioenergy).