Vermouth is a fortified wine flavored with aromatic herbs and spices ("aromatized" in the trade) in recipes that are closely guarded trade secrets.
The inventor, Antonio Benedetto Carpano from Turin, chose this name in 1786 because he was inspired by a German wine fortified with wormwood, a herb most famously used in distilling absinthe. The modern German word Wermut means both wormwood and vermouth. The herbs were originally used to mask raw flavors of cheap wine, imparting a slightly medicinal "tonic" flavor.
There are three styles of vermouth, in order from driest to sweetest: dry, sweet/red, and bianco/white. The sweet red vermouth is drunk as an apéritif, often straight up, as well as in mixed drinks like The Manhattan. Dry white vermouth, along with gin or vodka, is a key ingredient in the mixing of martinis, in proportions that may account for the lackluster sales of dry white vermouths. Sweet red vermouth is combined with whiskey and a maraschino cherry to create a "Manhattan cocktail." A sweet white vermouth is also made.