A martini is a cocktail made with gin and vermouth, served straight up with an olive or lemon twist garnish. A common variation, the vodka martini, uses vodka instead of gin. The typical ratio is two parts spirit to one vermouth.
A dry martini is one that has less vermouth, since even a dry vermouth has some sweetness. A dirty martini is one that includes a small amount of green olive brine to add a savory flavor. Green olives, sometimes stuffed with a pimiento, are traditional for dry martinis. When pickled cocktail onions are used as a garnish, the drink is called a Gibson.