A play sister is a very good friend or relative who you consider to be just like a sister.

A cultural and aesthetic mind-state that prioritizes making money, even as an “underground” or “radical” creator. The work isn’t made for money, but it’s the money that matters the most.

The undercover love interest of a man who is engaging another woman outside his marriage or relationship. To his wife or girlfriend, this extra girl is a friend, when the truth is he and this "play sister" may have been intimate in the past, but the relationship did not work out.