What is the French term, used to refer to courtesans of the nineteenth-century?

I recently finished reading a book entitled "Grandes horizontales : the lives and legends of Marie Duplessis, Cora Pearl, La Pa�va and La Pr�sidente" by Virginia Rounding. In the text of the book Mrs. Rounding uses a French term (starting with "de") to describe the lifestyle of the courtesans, which means existing in two worlds (or in one world in which everything is not what it appears) and is roughly translated into "twilight." As I cannot find the book at this time I was hoping that someone might be able to tell me what the word is. Thanks.