The short answer used to be 'Parfum' but today the answer is a little more varied and nuanced, as you can see below:
Parfum
This is the 'crème de la crème' of fragrances!
This is the most concentrated perfume category. It is also sometimes known as Extrait or 'Pure Perfume'.
The fragrance concentration level can be as high as 30% but typically it is around 20%.
You may reasonably expect for a Parfum to last about 6-8 hours on you and you should not have to top up during the middle of the day.
Parfums tend to be the most expensive and the size of the bottles tend to be the smallest.
In most cases, they are being offered in a stopper bottle (instead of spray) and frequently they are oil based (instead of alcohol). This allows a Parfum to be applied sparingly and precisely to certain points of the body, e.g. pulse or neck. The use of an oil base (instead of alcohol) also allows the perfume to last longer, as alcohol stimulates the diffusion of perfume.
Eau de Parfum
Eau de Parfums are the second highest in terms of concentration.
For most people, this has become the 'go-to' concentration when shopping for perfume.
Commonly, it contains 12 - 18% of pure perfume oil in alcohol. These tend to be sprays.
You may expect an Eau de Parfum to last about 4 - 5 hours on you, essentially half a day and ideal when you are going out for the evening.
Eau de Parfum Intense
These are quite a recent development and a combination of the dosage of a Parfum with the formula of an Eau de Parfum.
What does this actually mean?
The perfume concentration levels are 20-30% but the fragrances is diluted in alcohol and presented as a spray.
It was particularly the North American and Middle Eastern consumer who requested the creation of these products.
Here at Pairfum London, all of our perfumes are 'Eau de Parfum Intense', as we love the combination of the intensity and longevity of a Parfum with the freshness and ease of use of an Eau de Parfum.
Most customers tell us that our Eau de Parfums last the full day and that they are delighted with how much longer they last, than what they are used to.
Eau de Toilette
Eau de Toilettes are the most popular fragrance concentration.
It is a light spray with 5 - 15% of pure perfume in alcohol.
Expect it to last for about 2 - 3 hours. In other words, a mid-day top up will be required, which is why travel sizes have become very popular, i.e. they conveniently fit into bags.
Due to the lower concentration, they are also ideal for combining or layering fragrance.
Eau de Cologne
This is the oldest term for perfume and they are usually sprays.
They are light and fresh. The fragrance oil concentration level is 2 - 4% in either alcohol, water or a mix of these.
The scent usually lasts for about 1 - 2 hours.
Colognes tend to be the first fragrance used by the younger generation but they are also very popular in Latin America for a quick freshen up.
In North America, Cologne is used synonymously for 'After Shave' or 'masculine' perfumes.
After Shave
Essentially the same as an Eau de Cologne but specifically developed for men.
They became popular with men as part of their shaving or grooming routine and may contain additional skin care ingredients.
Eau Fraiche
This is the most diluted version of fragrance.
It typically contains about 1 - 3% of perfume, either in alcohol, water or a mix of the two. The alcohol level tends to be lower, i.e. more water.
The fragrance usually lasts for less than an hour.
Other common names for 'Eau Fraiche' are 'Spritzer' or 'Splash Cologne'.
History
The classification we have presented above (Parfum, EDT, EDP, etc…) are not an official but a historically evolved system to guide consumers by indicating a fragrance strength.
This system does not, however, take into account the quality of the ingredients used, which has a most significant impact on the longevity and strength of a fragrance.