Mistress is an old form of address for a woman. It implies "lady of the house", especially a woman who is head of a household.

An example is Mistress Quickly

Mistress Quickly

Mistress Quickly is an inn-keeper who appears in four plays by William Shakespeare:*Henry IV, Part 1*Henry IV, Part 2*Henry V*The Merry Wives of Windsor...

 in Shakespeare's The Merry Wives of Windsor

The Merry Wives of Windsor

The Merry Wives of Windsor is a comedy by William Shakespeare, first published in 1602, though believed to have been written prior to 1597. It features the fat knight Sir John Falstaff, and is Shakespeare's only play to deal exclusively with contemporary Elizabethan era English middle class life...

. The title did not necessarily distinguish between married and unmarried women.

The title Mrs.

Mrs.

Mrs or Mrs. is a honorific used for women, usually for those who are married and who do not instead use another title, such as Dr, Lady, or Dame. In most Commonwealth countries, a full stop is not used with the title...

 is an abbreviation of Mistress, and the titles Miss

Miss

Miss is an English language honorific traditionally used only for an unmarried woman . Originating in the 17th century, it is a contraction of mistress, which was used for all women. A period is not used to signify the contraction...

 and Ms.

Ms.

Ms. or Ms is an English honorific used with the last name or full name of a woman. According to The Emily Post Institute, Ms...

are also derived from it.