Titles are a part of language used to address people, which often also indicate the gender identity of the person being addressed.
Common formal titles include “Mr.” for men, and “Ms,” “Miss,” or “Mrs.” for women. Women’s titles are often designated based a marital status, but some women have preferences for specific titles that do not correspond to such status.
Some titles are gender-neutral but indicate profession or societal standing, such as Doctor, Professor or President. However, these titles are only available to those with the relevant background, qualifications and/or employment. Other titles indicate both position and gender identity, such as Duke/Duchess in the aristocracy, or Brother/Sister in religious orders.
People with non-binary gender identities often wish to be addressed with a gender-neutral title. One example of such a title is “Mx.” (most often pronounced “mix”), which is used as a gender-neutral equivalent of Mr./Mrs./Miss/Ms.