When Should You Use Miss, Mrs., or Ms.?
Using the honorifics Miss, Ms., or Mrs. used to be a common way to address women in a formal or business setting. But as more awareness grows around nonbinary gender identities and gender neutral pronouns and titles, these terms are becoming more and more outdated and unnecessary. However, there are ways to use the titles Miss, Ms., or Ms. without making a potentially embarrassing or disrespectful mistake.
Avoid going into any conversation making assumptions about a person's gender or their preferred titles or pronouns. The best way to make sure you use the right words when introducing someone is to simply ask them what they prefer.
If you're introducing someone to a crowd in public, then be sure to speak with them ahead of time about their preference of honorific (if any). In person-to-person business introductions, you can simply ask, "how would you like to be addressed?" if you don't already know.
You can also just skip the titles altogether and simply use a person's name when introducing them.
The Traditional Uses of Miss, Ms. and Mrs.
Traditionally, people addressed young girls as "miss." They also addressed an unmarried woman as "miss," but then "Ms." became more acceptable.
Feminists first began promoting the use of the term "Ms." for women as the female counterpart to "Mr." back in the 1950s, and it gained steam in the 1970s. It can be used by any adult woman regardless of her marital status, but it refers to adult women, not girls. It was almost always better to err on the side of "Ms." if you were unsure of the woman's preferred title or marital status.
The term "Mrs." originated to refer specifically to married women, but some women prefer to keep the "Mrs." in their names even after divorce and particularly if they're widowed. It's not safe to assume that all women using "Mrs." as a title have a current or living spouse, nor is it safe to look for a wedding ring. Most women wear them, but not all do—particularly if they'd divorced, separated, or widowed. They still might want to be addressed as "Mrs."
There's no standard for spelling for "Mrs." in the English language, although both "missus" and "missis" appear in literature.
A Historical Perspective
The title "mistress" is the feminine form of "mister," but it's virtually never used these days. As is the case with "mister," "mistress" was traditionally considered to be marital-status neutral. It was used to refer to both married and unmarried women.
Eventually, "mistress" was split into two separate contractions to distinguish the marital status of the woman in question. "Miss" denoted an unmarried woman while "Mrs."—the abbreviation for "missus"—applied to married women. Women then moved back toward a less-identifying term once again, adopting "Ms." to include all adult women regardless of marital status.
"Mistress" is now generally interpreted to mean a woman who is having an affair with a married man, so it's best to strike this term altogether from your business vernacular.
Never use the term "mistress" to identify or introduce a woman in the U.S. because it has a completely different meaning today than it did years ago, particularly in a business setting.
In 2017, Merriam-Webster added the gender-neutral honorific Mx. to its dictionary to recognize it as a title "for those who do not identify as being of a particular gender, or for people who simply don't want to be identified by gender."
Its pronunciation sounds like "mix" or "mux." People are increasingly using it in the United Kingdom, but its use isn't growing as quickly in the U.S.
Other gender-neutral options to using Mrs., Ms., or Miss include M., Ind. (for individual), and there are many more that aren't as common.