Eau De Toilette, Eau De Parfum, Eau de what!?

I've asked the very same question plenty of times when I was new to the world of perfumes, and I get it plenty of times now from others. A vast majority of perfumes even today are made in France (or may have roots in France even if made elsewhere). Even for perfumes made outside of the Francophone region, a few things still remain convention to label in French.

Most perfumes will label ingredients in both French and English, referring to water as "Aqua", and the fragrance oils that give the mixture its scent as "Parfum" for example. However, the most visible and ubiquitous use of French terms is for concentration. The relative concentration of the aromatic oils and compounds in a given fragrance is what the "Eau De" term indicates. Generally, the higher the concentration, the longer a perfume will last on skin, and in many cases may have stronger notes.

The terminology is quite imprecise, and the only reasonably straightforward comparisons are between two concentrations of the same fragrance, from within the same house. Here's the most common terminology I've come across:

Eau De Cologne ("Water of Cologne" in literal translation), abbreviated to EdC is generally the most dilute form of a fragrance with a proper term for it. It may be anywhere between 3-8% aromatic compounds. Typically, Eau De Cologne concentration is used for male fragrances, and these will usually not have a very long life on the skin. Many colognes tend to be based on citrus accords.

Eau De Toilette (EdT) is the next one up. And this is where things get really interesting. EDTs can contain anywhere from 5-15% aromatic compounds, leading to a huge amount of variation in their potency and longevity. They overlap EdC on the lower end, and EdPs on the upper end of their concentration.

Eau De Parfum (EdP) is the next concentration in line. These can have between 10-20% aromatic compounds, and hence the overlap between EdPs from some houses and EdTs from others. Generally, EdP is a concentration seen for most female fragrances, although a few exceptions exist on the masculine side too, such as Essenza (Armani), Dior Homme Intense (Dior), Terre D'Hermes Parfum (Hermes).

It would be misleading to say EdTs don't as long as the higher concentrations as a generalisation. While a lower concentration of the same fragrance from within the same range will necessarily be less potent than a higher concentration, the same cannot be said when comparing across houses or ranges. For example, Chanel's Antaeus for Men is an EdT, but is much more potent in my perception than Armani's Essenza, which is an EdP.

For male fragrances,  manufacturers seem reluctant to use the term Eau De Parfum, even though many are potent enough to be more than a match for most EdPs. For example, Chanel's Antaeus and Eau Extreme are both strong enough to be labelled EdP were they feminine. Whether it's a case of the makers fearing the "EdP" term being associated with feminine fragrance and perception of less masculine character in the scent by the buyer, or simply intertia, I can't say.

Essense De Parfum (ESdP) is a seldom-seem concentration that sits vaguely in between Pure Parfum and Eau De Parfum. These can have 15-30% aromatic compounds, and generally this concentration is always more potent than a corresponding EdT or EdP. This concentration is rare to say the least; so far in mainstream fragrances, I have only seem J'Adore L'Or (Dior), Miss Dior Le Parfum (Dior) and Parisienne L'Essentiel (YSL) in this concentration.

Pure Parfum or Extrait De Parfum can have anywhere from 15% to 40% (or even higher) aromatic compounds. Usually sold as dab-ons (most commonly seen in my experience in Chanel, who sell extrait versions of a fair few of their fragrances), these are generally very potent, and have the longest life on skin compared to lower concentrations of the same scent. These also tend to be very pricey (Australian UVPs can exceed $20/ml), and don't evaporate on exposure to the air very quickly.

There's another couple of concentrations used by some manufacturers that don't make appearances often enough to be common usage.

The word Légère is sometimes added to the concentration to indicate a lighter version of a fragrance. For example, Opium Vapeurs De Parfum (YSL) is listed as an "EdT Légère", which means it is lighter than what an EdT would otherwise be for the the same fragrance from YSL. Similarly, Lancome's La Vie Est Belle Légère is a lighter (softer) version of the same fragrance. A Légère EdP would be roughly in between what an EdT and EdP would be for the same perfume.

The world L'Absolu is the opposite in perfume terms of Légère. It indicates the more concentrated, or more often the version of a fragrance with more intense notes. Tresor L'Absolu (Lancome), and J'Adore L'Absolu (Dior) are prime examples. Both are more potent and have differing, stronger notes than their "normal" counterparts.

Armani and a few other houses use the term "Intense" after the concentration for fragrances more potent that the classification would typically indicate, but not enough to move up a notch to the next in line. This is a very grey area though; what Armani calls EdTI (EdT Intense) might be an EdP if another house were to sell it. Armani's Privé lineup has the black bottles labelled as "EdP Intense", which are again more potent than other Armani EdPs, but well short of being EsDPs.

Chanel uses the term EdT Concentré for Eau Extreme, which to me is a synonym for an EdP. I strongly suspect the only reason it's labelled as such is to keep the EdT terminology across their male lineup, even if in variants to avoid going the EdP way of labels. In terms of strength of the fragrance and its longevity, it blows most EdPs clean out the water.

While the common perception that extraits will be more potent than EsDPs, which in turn will be more concentrated than EdPs, which will be stronger than EdTs and EdCs is not necessarily false, it is not entirely true either when it comes to EdP and lower potencies. While an EdP of one fragrance will be stronger than an EdT of the same fragrance, it may not necessarily be the case across different fragrances.

Concentration has a direct relation to price; usually the higher the concentration, the more expensive a perfume will be. Which is partially explanatory towards female fragrances (generally EdPs) being costlier than their male counterparts (which are usually EdT).

In concentrations lower than extrait, EdPs and EdTs have plenty of overlap, and just being an EdP will not necessarily mean better projection or longevity. Moreover, sillage/projection (how far a scent trails around you) and longevity (how long it stays on the skin once applied) are not related to each other. It is very possible to have a fragrance that has very long life on the skin but doesnt necessarily project too far away from you; L'Instant De Guerlain (Guerlain) is a prime example. On the other hand, you can have fragrances that project very well but wear off very quickly.