Said to have been named after the company of Martini & Rossi (famous for their vermouth), this cocktail is made with gin and vermouth, garnished with either a green olive or a lemon twist. The less vermouth it contains, the "drier" (see dry) it is. A martini may be served straight up or on the rocks. It may also be made with vodka, in which case it's called a vodka martini. A gibson is a martini garnished with a tiny white onion.