Vinegar is chemically

Concept — Household liquids are named for how they are used, not for what they are made of; chemically each is a definite compound present at a definite concentration. Carboxylic acids are the family of organic acids built on the –COOH group: its one-carbon member is methanoic (formic) acid, HCOOH, and its two-carbon member is ethanoic (acetic) acid, CH3COOH. Concentration is part of the chemical identity — the same acid is called dilute when it is only a few percent in water, and glacial when it is essentially pure.

Application — Vinegar is the sour liquid produced when the ethanol in a fermented liquor is oxidised in air by Acetobacter bacteria:

CH3CH2OH + O2 → CH3COOH + H2O

The liquid sold and used as vinegar is that product in water — typically a 4–8% aqueous solution of ethanoic acid, that is, dilute acetic acid. Because ethanoic acid is a weak acid it ionises only partially, so vinegar sits at a pH of about 2.4–3.4 with a sharp sour taste, not at the near-zero pH a strong mineral acid of the same concentration would give.

Cross-check — set each named substance against that composition:

Result — Vinegar is chemically dilute acetic acid: a roughly 4–8% aqueous solution of ethanoic acid, CH3COOH. Pure ethanoic acid, which freezes below 16.6 °C into ice-like crystals, is called glacial acetic acid and is a different preparation from vinegar.