What is "placage" as it is described in the text?

"Plaçage" is the term given to the practice, unique to New Orleans, of a wealthy and influential white man giving financial support and a degree of social status to his non-white mistresses and their children. The women who benefitted from plaçage considered themselves, and were often considered by white citizens, as being of a higher class than poorer, less advantaged, so-called "pure" whites like the Irish-ancestored Mrs. Hanrahan. Delphine is a second generation descendant of plaçage, her black grandmother having chosen a powerful white man and given birth to Delphine's mother, who herself chose a similarly powerful white man and subsequently gave birth to Delphine (see "Quotes," p. 129).