These terms refer to the strength of the fragrance, or more specifically, to how much high grade alcohol and/or water has been added to the fragrance oils. Parfum (generally the most concentrated form you can buy) has 15-25% perfume oil dissolved in alcohol.
Eau Fraiche (Usually 3% or less perfume oil)
EDC - Eau de cologne (2 - 5% perfume oil)
EDT - Eau de toilette (4 - 10% perfume oil)
EDP - Eau de parfum (8 - 15% perfume oil)
Soie de Parfum (15 - 18% perfume oil)
PARFUM or Perfume (15 - 25% -- also sometimes referred to as extract or extrait)
Perfume oil (15-30% perfume oil in an oil rather than alcohol base)
Parfum de Toilette: Most companies use this term to describe a concentration that is either the same as EDP, or between EDP and Parfum. However, some companies use the term to describe an EDT concentration, so beware
Some companies also use different notes, or different proportions of notes, in the different forms of fragrance they offer.