So exactly what is the difference between eau de toilette, eau de parfum, and the other fragrance forms? 

Here is a generalized list of the different concentrations available:

Perfume (Parfum) - This consists of a 15-30% concentration of perfume essence and is the strongest perfume fragrance available. This means that not only do you need to use less, but also that the fragrance lasts longer, typically for up to 6 hours, depending on skin type.

Parfum De Toilette -This is usually between a perfume fragrance and an EDP in strength but a few companies use the term to describe an EDT.

Eau De Parfum (EDP) - This is lighter than Perfume, with an 8-15% concentration, and so is less expensive but still has long lasting characteristics, from 3 to 5 hours.

Eau De Toilette (EDT) - This is a lighter more delicate perfume fragrance, with a 4-8% concentration of the essence, and is therefore most suited to everyday use. It is normally less expensive than Eau de Parfum, and lasts for 2 to 4 hours.

Eau De Cologne (EDC) - This is often referred to just as Cologne and has the greatest dilution of fragrances with a 3-5% concentration of perfume essence, lasting up to 2 hours.

Eau De Toilette (EDT) For Men - This has the greatest concentration of essence generally available for men and hence lasts the longest, up to 5 hours. It is often available in either a splash or a spray.

Aftershave - Less strong, it is the most popular choice and lasts for 2 to 3 hours. Aftershaves are kinder to the skin than EDT's. Those with very sensitive skin should use aftershave balms.