Demimonde is a polite 19th century term that was often used the same way we use the term "mistress" today. In the 19th century, however, it primarily referred to a class of women on the fringes of respectable society supported by wealthy lovers (usually each had several). The term is also used to refer to these women as a group, and the social circles they moved in, which were at the fringes of respectable society.