Vermouth

A fortified wine flavored with botanicals — herbs, roots, bark and spices. It's wine-based rather than a distilled spirit, which is why it's much lower in alcohol, usually 15–18%.

Sweet (red) vermouth is richer and spiced, and goes into a Manhattan or Negroni. Dry (white) vermouth is crisp and herbal, and goes into a martini. They aren't interchangeable.

Yes — this is the one most people get wrong. Because it's wine-based, vermouth oxidizes once opened. Refrigerate it and use dry vermouth within about a month, sweet within roughly six weeks. Left in a cabinet it goes flat and sour in a couple of weeks.

Drink it on its own over ice with a twist — that's how it's enjoyed in Europe. It also works beautifully as a cooking wine in pan sauces and risotto.