Bottles of some notable commercial perfumes: (clockwise from top left) Bois De Violette, Serge Lutens, 1992; Angel, Thierry Mugler, 1994; Shalimar, Guerlain, 1925; Beyond Paradise, Estée Lauder, 2003; No. 5, Chanel, 1921 (Pre-1950 bottle); Cabochard, Parfums Grès, 1959 (original bottle); Bellodgia, Caron, 1927; Arpège, Lanvin, 1927 (original bottle); Nombre Noir, Shiseido, 1981; Mitsouko, Guerlain, 1919; Pour Un Homme, Caron, 1934.Describing a perfume
 
Shelves of perfumesThe precise formulas of commercial perfumes are kept secret. Even if they were widely published, they would be dominated by such complex chemical procedures and ingredients that they would be of little use in providing a useful description of the experience of a scent. Nonetheless, connoisseurs of perfume can become extremely skillful at identifying components and origins of scents in the same manner as wine experts .

The most practical way to start describing a perfume is according to its concentration level, the family it belongs to, and the notes of the scent, which all affect the overall impression of a perfume from first application to the last lingering hint of scent

Concentration levels
Perfume oil is necessarily diluted with a solvent because undiluted oils (natural or synthetic) contain high concentrations of volatile components that will likely result in allergic reactions and possibly injury when applied directly to skin or clothing.

By far the most common solvent for perfume oil dilution is ethanol or a mixture of ethanol and water. Perfume oil can also be diluted by means of neutral-smelling lipids such as jojoba, fractionated coconut oil or wax. The concentration by percent/volume of perfume oil is as follows:

Perfume extract: 20%-40% aromatic compounds
Eau de parfum: 10-30% aromatic compounds
Eau de toilette: 5-20% aromatic compounds
Eau de cologne: 2-5% aromatic compounds

Traditional
The traditional classification which emerged around 1900 comprised the following categories:

Single Floral: Fragrances that are dominated by a scent from one particular flower; in French called a soliflore. (e.g. Serge Lutens' Sa Majeste La Rose, which is dominated by rose.)
Floral Bouquet: Containing the combination of several flowers in a scent.
Ambery: A large fragrance class featuring the scents of vanilla and animal scents together with flowers and woods. Can be enhanced by camphorous oils and incense resins, which bring to mind Victorian era imagery of the Middle East and Far East.
Woody: Fragrances that are dominated by woody scents, typically of sandalwood and cedar. Patchouli, with its camphoraceous smell, is commonly found in these perfumes.
Leather: A family of fragrances which features the scents of honey, tobacco, wood and wood tars in its middle or base notes and a scent that alludes to leather.

 Modern
Since 1945, due to great advances in the technology of perfume creation (i.e., compound design and synthesis) as well as the natural development of styles and tastes; new categories have emerged to describe modern scents:

Bright Floral: combining the traditional Single Floral & Floral Bouquet categories.
Green: a lighter and more modern interpretation of the Chypre type.
Oceanic/Ozone: the newest category in perfume history, appearing in 1991 with Christian Dior's Dune. A very clean, modern smell leading to many of the modern androgynous perfumes.
Citrus or Fruity: An old fragrance family that until recently consisted mainly of "freshening" eau de colognes due to the low tenacity of citrus scents. Development of newer fragrance compounds has allowed for the creation of primarily citrus fragrances.
Gourmand: scents with "edible" or "dessert"-like qualities. These often contain notes like vanilla and tonka bean, as well as synthetic components designed to resemble food flavors. An example is Thierry Mugler's Angel.