.... is apparently French for "a thousand leaves". And also the name of a dessert mais non?
After having been describing my party dress in terms such as "Fru Fru, Flossy, Frothy, An Abundance Of Ruffles, You Know.... A Bit Like That Dress That Carrie Wore In The Paris Scene Right At The End Of The Series" I was pleased to learn that the official name for That Dress actually is The Mille-feuille Dress!
Where did I find this nugget of information? Why, in the official SATC The Movie book of course! So, according to Wikipedia I will be going to my 40th dressed as a custard slice - you can't get better than that!