Like a Hotwife or Slutwife, a Vixen is woman that initially agreed to being shared sexually by her husband with other people, predominantly other men, but also other women, to promote the sexual pleasure and increased experience for their husband, but then discovered her natural slut (sexually liberated unique treasure) behaviour, and now craves the sexual pleasure, freedom, and empowerment, being shared by her husband gives her.
A girl that likes to have sex without and transfer of money, however, since she is a sexy sweetheart you refuse to call her a whore, slut, skank, harlot, streetwalker, prostitute, or ho