A mistress is a long-term female lover and companion who is not married to her partner; the term is used especially when her partner is married. The relationship generally is stable and at least semi-permanent; however, the couple does not live together openly. Also the relationship is usually, but not always, secret. There is an implication that a mistress may be “kept”—i.e. , that the lover is paying for some of the woman’s living expenses.