Listerine is a brand name for antiseptic mouthwash, named after Joseph Lister (father of modern antisepsis). Its medicinal taste is palliated slightly by a sweet flavor. The slogan is, "Kills germs that cause bad breath."
Currently manufactured and distributed by Pfizer Inc, Listerine is one of the most popular mouthwashes (Scope being its main competitor). However, there is evidence that its properties as a solvent, mainly because of the 26.9% (in regular Listerine) alcohol, causes an easier reception of carcinogens. In other words, repeated use of Listerine increases the chance of oral cancer.
The active ingredients are menthol, thymol, methyl salicylate, and eucalyptol. Currently, other flavors include Cool Mint, FreshBurst, Natural Citrus, and Tartar Control (not really a flavor, but a separate type of Listerine mouthwash).
The Listerine brand name is also used on brands of toothpaste, dental floss, and PocketPaks, a minty, dissolvable strip used to instantly wash and refresh the mouth.