An alcoholic beverage made by floating several different ingredients on top of another in colorful layers. This aperitive drink originated in France and was introduced to the United States in New Orleans during the early 1800's. Most popular recipes are Buttery Nipple, Chocolate Monk, Rainbow Pousse-Cafe, and Traffic Light and are customarily served after dinner with coffee.
These drinks are contained in shot, cordial, or Pousse Cafe glasses. One must pay careful attention and refer to density charts for weight of liqueurs used in this layered drink. As far as I know, the liqueur with the heaviest density is poured in first, very slowly, and layers are seperated with a bar spoon, or a maraschino cherry for smaller glasses. Since the density of every liqueur varies, it is best to experiment.
Sources: dictionary.com, The New American Bartender's Guide; New Expanded Edition by John J. Poister