What it is and where it comes from
Vinegar is made in two steps: yeast turns sugar into alcohol, then bacteria turn the alcohol into acetic acid. Once it is vinegar, it no longer intoxicates. The Prophet said "what an excellent condiment vinegar is" (Muslim). Acetic acid (E260) is the same acid.
Where you find it
Pickles, ketchup, mayonnaise, mustard, dressings, crisps and sauces.
What to look for on the label
Spirit, cider, malt, rice and fruit vinegars are halal. For wine vinegar and balsamic vinegar, see wine vinegar.
This is a guide, not a fatwa. Recipes change, so check the label, look for halal certification, and ask your local imam where scholars differ.