All About Liqueurs, Cordials & Aperitifs

Liqueurs, Schnapps, Anise, and Bitters are terms that cover a wide variety of types of spirits. What they all share in common is that they are flavored spirits.
Liqueurs (also known as Cordials) are sweet, flavor-infused spirits that are categorized according to the flavoring agent (i.e., fruits, nuts, herbal and spice blends, creams and such). The word liqueur comes from the Latin liquifacere ("to dissolve") and refers to the dissolving of flavorings in the spirits. Artificial flavorings are strictly regulated in most countries, and where allowed, must be prominently labeled as such.
Top-quality liqueurs are produced by distillation of either the fermented flavor materials or the spirit in which they have been infused. Many liqueurs use finished spirits such as Cognac, Rum or Whisky as their base. Others macerate fruit or other flavorings in a neutral spirit. Crèmes (crème de menthe, crème de cacao, etc.) are liqueurs with a primary flavor (a single, dominant flavor rather than a mix), while cream liqueurs combine dairy cream and alcohol in a homogenized, shelf-stable blend.
All liqueurs are blends, even those with a primary flavor. A touch of vanilla is added to crème de cacao in order to emphasize the chocolate. Citrus flavor notes sharpen the presentation of anise. Herbal liqueurs may contain dozens of different flavor elements that a master blender manipulates to achieve the desired flavor profile.
Liqueurs are not usually aged for any great length of time (although their base spirit may be), but may undergo resting stages during their production in order to allow the various flavors to "marry" into a harmonious blend.

Liqueurs can be hard to classify, but regardless of flavor they can be broadly divided into two categories.
Generics are liqueurs of a particular type (Crème de Cacao or Curaçao, for example) that can be made by any producer.
Proprietaries are liqueurs with trademarked names that are made according to a specific formula. Examples of such liqueurs include Kahlúa, Grand Marnier, and Southern Comfort.
Schnapps is a general term used for an assortment of white and flavored spirits that have originated in northern countries or regions such as Germany or Scandinavia. Schnapps can be made from grain, potatoes, or molasses and be flavored with virtually anything (Watermelon and Root Beer Schnapps from the United States being proof of that). The dividing line between Schnapps and Flavored Vodka is vague and is more cultural than stylistic, although European Schnapps tend to be drier than their American counterparts and liqueurs.
Anise-Flavored Spirits can vary widely in style depending on the country of origin. They can be dry or very sweet, low or high proof, distilled from fermented aniseed or macerated in neutral spirit. In France, Anis (as produced by Pernod) is produced by distilling anise and a variety of other botanicals together. Pastis is macerated, rather than distilled, and contains fewer botanicals than Anis. In Italy, Sambucca is distilled from anise and botanicals, but is then heavily sweetened to make it a liqueur. Oil of fennel (also known as green anise) is frequently added to boost the aroma of the spirit. Greece has a drier, grappa-like liqueur called Ouzo , which is stylistically close to pastis.
Bitters are the modern-day descendents of medieval medical potions and are marketed as having at least some vaguely therapeutic value as stomach settlers or hangover cures. They tend to be flavored with herbs, roots, and botanicals, contain lower quantities of fruit and sugar than liqueurs, and have astringent notes in the palate.