Acetic acid /əˈsiːtɪk/, systematically named ethanoic acid /ˌɛθəˈnoʊɪk/, is an acidic, colourless liquid and natural compound with the chemical system CH3COOH (also written as CH3CO2H, C2H4O2, 5 Step Formula or HC2H3O2). Vinegar is not less than 4% acetic acid by quantity, making acetic acid the principle component of vinegar aside from water. Historically, vinegar was produced from the third century BC and was likely the primary acid to be produced in giant quantities. Acetic acid is the second easiest carboxylic acid (after formic acid). It is an important chemical reagent and industrial chemical across various fields, used primarily in the production of cellulose acetate for photographic film, polyvinyl acetate for wooden glue, and artificial fibres and fabrics. In households, diluted acetic acid is usually used in descaling agents. Within the meals trade, acetic acid is managed by the food additive code E260 as an acidity regulator and as a condiment. In biochemistry, the acetyl group, derived from acetic acid, simple income method is fundamental to all forms of life.

When sure to coenzyme A, it's central to the metabolism of carbohydrates and 5 Step Formula fats. The global demand for acetic acid as of 2023 is about 17.88 million metric tonnes per year (t/a). Many of the world's acetic acid is produced via the carbonylation of methanol. Its production and subsequent industrial use poses health hazards to workers, together with incidental skin damage and chronic respiratory injuries from inhalation. The trivial title "acetic acid" is the most commonly used and most well-liked IUPAC identify. The systematic identify "ethanoic acid", a legitimate IUPAC title, is constructed based on the substitutive nomenclature. The identify "acetic acid" derives from the Latin phrase for vinegar, "acetum", which implies "to bitter" in relation to the bitter style of fermented fruits. Similar to the German name "Eisessig" ("ice vinegar"), the name comes from the solid ice-like crystals that type with agitation, barely under room temperature at 16.6 °C (61.9 °F). Acetic acid can by no means be truly water-free in an ambiance that incorporates water, so the presence of 0.1% water in glacial acetic acid lowers its melting point by 0.2 °C.

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