Acetic acid, with the chemical formula CH3COOH, also known as ethanoic acid, is the simplest organic monobasic weak acid after formic acid (pKa = 4.75 at room temperature). At standard temperature and pressure, it is a colorless liquid with a pungent odor, often represented by the symbols HOAc or HAc, and is the main component of vinegar.

Acetic acid is widely distributed in nature; for example, it exists in the form of ethyl acetate in fruits, vegetables, and vegetable oils, as a free acid in animal tissues, excretions, and blood, and can also be produced through the fermentation and transformation of other organic compounds by microorganisms.