It’s all about concentration!
Each perfume house uses their own terminology and categories to classify their perfumes according to the concentration of essences or aromatic oils they contain, but the following should give you a general idea of what you’re buying:
Perfume contains the strongest concentration of essences and oils (up to 25%) which makes it the longest lasting and the most intense of all the scent (also the most expensive).
Eau de Parfum
It contains a lower concentration of scent ingredients (15-20%) than traditional perfumes.It is less intense than perfume extract and that’s why it is also cheaper
Eau de Toilette
With a lower concentration of fragrance compound (5-15%), eau de toilettes are more subtly scented versions of the original perfumes. It’s refreshing when applied but fades away quite quickly so you need to reapply every couple of hours.
The least concentrated form of fragrance containing only 2-5% essential perfume oils and for that reason can be used more generously.
It is extremely refreshing in hot weather months and and can be frequently reapplied when needed.
Most people refer to colognes when they describe any fragrance for men. That’s not very “scientific” approach but if you like the smell, who cares about the concentration :)