Vinegar

Aqueous acetic acid solution made by a two-step fermentation, alcoholic then acetic, of sugary liquids.

Characteristics

Table vinegar usually contains 4 to 8 % acetic acid.
Distilled white vinegar has a pH of about 2.6.
Cider, wine and other vinegars exist, with traces of aromatic compounds.
Approved in the EU as a basic substance, at most 10 % acetic acid (Regulation (EU) 2015/1108).

Role in the preparation: It is used as an acidifying agent to adjust the pH of the water or of the preparation.

Caution: Above 10 % acetic acid it is corrosive to skin: wear gloves and goggles, never mix it with bleach, and keep it labelled.

Sources: Vinegar - Wikipedia · Commission Implementing Regulation (EU) 2015/1108 approving the basic substance vinegar (consolidated) - EUR-Lex

Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.