In modern times the word “mistress” is used primarily to refer to the female lover of a man who is married to another woman; in the case of an unmarried man, it is usual to speak of a “girlfriend” or “partner”. The term was originally used as a neutral feminine counterpart to “mister” or “master”.
In a long-term relationship with her attached lover, and is often referred to as the other woman. Generally, the relationship is stable and at least semi-permanent, but the couple does not live together openly and the relationship is usually, but not always, secret. There is often also the implication that the mistress is sometimes “kept” – i.e. that her lover is contributing to her living expenses.
A mistress is usually not considered a prostitute: while a mistress, if “kept”, may, in some sense, be exchanging sex for money, the principal difference is that a mistress has sex with fewer men and there is not so much of a direct quid pro quo between the money and the sex act. There is usually an emotional and possibly social relationship between a man and his mistress, whereas the relationship between a prostitute and their client is predominantly sexual. It is also important that the “kept” status follows the establishment of a relationship of indefinite term as opposed to the agreement on price and terms established prior to any activity with a prostitute.
Historically the term has denoted a “kept woman”, who was maintained in a comfortable (or even lavish) lifestyle by a wealthy man so that she would be available for his sexual pleasure. Such a woman could move between the roles of a mistress and a courtesan depending on her situation and environment.
In modern times the word “mistress” is used primarily to refer to the female lover of a man who is married to another woman; in the case of an unmarried man, it is usual to speak of a “girlfriend” or “partner”. A woman who is skilled in a particular subject or activity. (possibly sexually)