Generally speaking, it is considered proper etiquette to use Mrs. to refer to married women, Miss to refer to unmarried women and young girls, and Ms. to refer to a woman of unknown marital status or when marital status is irrelevant.

Mr., Mrs., Miss, and Ms.: What They Mean And How To Use Them

Mrs. originated as a contraction of the honorific Mistress (the feminine of Mister or Master) which was originally applied to both married and unmarried women in the upper class. Writers who used Mrs for unmarried women include Daniel Defoe, Samuel Richardson, Henry Fielding, and Samuel Johnson.

Mrs. is a title used for a married woman. The more neutral title Ms. can be used instead for a woman whose marital status is unknown or irrelevant or who expresses a preference for this mode of address.

Mrs. (pronounced MIS–iz) is similar to Miss, except that it refers to a married woman. The other difference is that Mrs. is not used as a stand-alone title; to be polite in addressing a married woman without including her last name, speakers of American English would often refer to her as ma’am.

Ms., Mrs., or Miss: Which One Should You Use? - The Blue Book of ...

Mrs. is a traditional title used for a married woman. Miss is a traditional title used for an unmarried woman. Mx. is a title that indicates neither marital status nor gender. Miss, when attached to a name, is a traditional title of respect for a girl or unmarried woman.